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 $237.95   11.749%   $265.9067   $265.91   $265.90   $265.90  
  Purchase #2 $230.80   8.355%   $250.0833   $250.08   $250.10   $250.10  
  Purchase #3 $236.44   4.562%   $247.2264   $247.23   $247.25   $247.20  
  Purchase #4 $16.39   8.528%   $17.7877   $17.79   $17.80   $17.80  
  Purchase #5 $250.77   4.730%   $262.6314   $262.63   $262.65   $262.60  
  Purchase #6 $241.82   13.131%   $273.5734   $273.57   $273.55   $273.60  
  Purchase #7 $165.98   6.668%   $177.0475   $177.05   $177.05   $177.00  
  7 purchase totals = $1,380.15       $1,494.2564   $1,494.26   $1,494.30   $1,494.20