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 $235.64   4.196%   $245.5275   $245.53   $245.55   $245.50  
  Purchase #2 $228.28   12.732%   $257.3446   $257.34   $257.35   $257.30  
  Purchase #3 $125.30   4.536%   $130.9836   $130.98   $131.00   $131.00  
  Purchase #4 $80.26   3.438%   $83.0193   $83.02   $83.00   $83.00  
  Purchase #5 $8.89   12.276%   $9.9813   $9.98   $10.00   $10.00  
  Purchase #6 $184.96   8.632%   $200.9257   $200.93   $200.95   $200.90  
  Purchase #7 $23.38   3.793%   $24.2668   $24.27   $24.25   $24.30  
  7 purchase totals = $886.71       $952.0488   $952.05   $952.10   $952.00