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 $46.97   10.299%   $51.8074   $51.81   $51.80   $51.80  
  Purchase #2 $218.80   12.712%   $246.6139   $246.61   $246.60   $246.60  
  Purchase #3 $24.74   10.272%   $27.2813   $27.28   $27.30   $27.30  
  Purchase #4 $225.78   3.213%   $233.0343   $233.03   $233.05   $233.00  
  Purchase #5 $44.78   12.628%   $50.4348   $50.43   $50.45   $50.40  
  Purchase #6 $67.67   10.807%   $74.9831   $74.98   $75.00   $75.00  
  Purchase #7 $31.88   10.309%   $35.1665   $35.17   $35.15   $35.20  
  7 purchase totals = $660.62       $719.3213   $719.31   $719.35   $719.30