Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $188.88   13.871%   $215.0795   $215.08   $215.10   $215.10  
  Purchase #2 $227.25   10.819%   $251.8362   $251.84   $251.85   $251.80  
  Purchase #3 $168.47   3.449%   $174.2805   $174.28   $174.30   $174.30  
  Purchase #4 $149.93   5.391%   $158.0127   $158.01   $158.00   $158.00  
  Purchase #5 $223.44   10.806%   $247.5849   $247.58   $247.60   $247.60  
  Purchase #6 $184.48   9.305%   $201.6459   $201.65   $201.65   $201.60  
  Purchase #7 $107.40   10.635%   $118.822   $118.82   $118.80   $118.80  
  7 purchase totals = $1,249.85       $1,367.2617   $1,367.26   $1,367.30   $1,367.20