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 $227.67   10.572%   $251.7393   $251.74   $251.75   $251.70  
  Purchase #2 $245.36   7.702%   $264.2576   $264.26   $264.25   $264.30  
  Purchase #3 $34.44   9.751%   $37.7982   $37.80   $37.80   $37.80  
  Purchase #4 $23.89   6.281%   $25.3905   $25.39   $25.40   $25.40  
  Purchase #5 $85.58   10.158%   $94.2732   $94.27   $94.25   $94.30  
  Purchase #6 $159.78   5.138%   $167.9895   $167.99   $168.00   $168.00  
  Purchase #7 $201.46   3.783%   $209.0812   $209.08   $209.10   $209.10  
  7 purchase totals = $978.18       $1,050.5295   $1,050.53   $1,050.55   $1,050.60