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 $182.65   10.559%   $201.936   $201.94   $201.95   $201.90  
  Purchase #2 $91.50   4.649%   $95.7538   $95.75   $95.75   $95.80  
  Purchase #3 $173.78   7.301%   $186.4677   $186.47   $186.45   $186.50  
  Purchase #4 $55.33   5.499%   $58.3726   $58.37   $58.35   $58.40  
  Purchase #5 $27.61   6.816%   $29.4919   $29.49   $29.50   $29.50  
  Purchase #6 $242.46   5.590%   $256.0135   $256.01   $256.00   $256.00  
  Purchase #7 $170.68   4.375%   $178.1473   $178.15   $178.15   $178.10  
  7 purchase totals = $944.01       $1,006.1828   $1,006.18   $1,006.15   $1,006.20