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 $194.86   4.245%   $203.1318   $203.13   $203.15   $203.10  
  Purchase #2 $29.71   12.232%   $33.3441   $33.34   $33.35   $33.30  
  Purchase #3 $210.72   6.390%   $224.185   $224.19   $224.20   $224.20  
  Purchase #4 $227.70   3.621%   $235.945   $235.95   $235.95   $235.90  
  Purchase #5 $250.35   4.690%   $262.0914   $262.09   $262.10   $262.10  
  Purchase #6 $10.81   7.485%   $11.6191   $11.62   $11.60   $11.60  
  Purchase #7 $23.57   5.813%   $24.9401   $24.94   $24.95   $24.90  
  7 purchase totals = $947.72       $995.2565   $995.26   $995.30   $995.10