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 $63.68   6.806%   $68.0141   $68.01   $68.00   $68.00  
  Purchase #2 $56.76   3.163%   $58.5553   $58.56   $58.55   $58.60  
  Purchase #3 $20.78   13.842%   $23.6564   $23.66   $23.65   $23.70  
  Purchase #4 $198.83   13.265%   $225.2048   $225.20   $225.20   $225.20  
  Purchase #5 $188.92   11.405%   $210.4663   $210.47   $210.45   $210.50  
  Purchase #6 $54.42   10.264%   $60.0057   $60.01   $60.00   $60.00  
  Purchase #7 $168.80   10.848%   $187.1114   $187.11   $187.10   $187.10  
  7 purchase totals = $752.19       $833.0140   $833.02   $832.95   $833.10