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 $120.74   11.272%   $134.3498   $134.35   $134.35   $134.30  
  Purchase #2 $191.34   9.123%   $208.7959   $208.80   $208.80   $208.80  
  Purchase #3 $70.57   8.134%   $76.3102   $76.31   $76.30   $76.30  
  Purchase #4 $60.42   5.792%   $63.9195   $63.92   $63.90   $63.90  
  Purchase #5 $19.30   7.837%   $20.8125   $20.81   $20.80   $20.80  
  Purchase #6 $244.59   8.168%   $264.5681   $264.57   $264.55   $264.60  
  Purchase #7 $94.77   6.768%   $101.184   $101.18   $101.20   $101.20  
  7 purchase totals = $801.73       $869.9400   $869.94   $869.90   $869.90