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 $53.71   8.808%   $58.4408   $58.44   $58.45   $58.40  
  Purchase #2 $206.59   6.324%   $219.6548   $219.65   $219.65   $219.70  
  Purchase #3 $154.53   10.777%   $171.1837   $171.18   $171.20   $171.20  
  Purchase #4 $15.83   12.442%   $17.7996   $17.80   $17.80   $17.80  
  Purchase #5 $169.36   12.163%   $189.9593   $189.96   $189.95   $190.00  
  Purchase #6 $139.33   8.527%   $151.2107   $151.21   $151.20   $151.20  
  Purchase #7 $208.69   12.556%   $234.8931   $234.89   $234.90   $234.90  
  7 purchase totals = $948.04       $1,043.1420   $1,043.13   $1,043.15   $1,043.20