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 $56.81   11.859%   $63.5471   $63.55   $63.55   $63.50  
  Purchase #2 $229.86   8.573%   $249.5659   $249.57   $249.55   $249.60  
  Purchase #3 $43.54   11.217%   $48.4239   $48.42   $48.40   $48.40  
  Purchase #4 $223.45   10.270%   $246.3983   $246.40   $246.40   $246.40  
  Purchase #5 $120.60   8.859%   $131.284   $131.28   $131.30   $131.30  
  Purchase #6 $6.68   11.664%   $7.4592   $7.46   $7.45   $7.50  
  Purchase #7 $120.55   4.449%   $125.9133   $125.91   $125.90   $125.90  
  7 purchase totals = $801.49       $872.5917   $872.59   $872.55   $872.60