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 $9.26   3.384%   $9.5734   $9.57   $9.55   $9.60  
  Purchase #2 $138.52   7.825%   $149.3592   $149.36   $149.35   $149.40  
  Purchase #3 $101.96   13.677%   $115.9051   $115.91   $115.90   $115.90  
  Purchase #4 $102.89   12.205%   $115.4477   $115.45   $115.45   $115.40  
  Purchase #5 $102.98   4.202%   $107.3072   $107.31   $107.30   $107.30  
  Purchase #6 $182.37   4.523%   $190.6186   $190.62   $190.60   $190.60  
  Purchase #7 $132.43   13.640%   $150.4935   $150.49   $150.50   $150.50  
  7 purchase totals = $770.41       $838.7047   $838.71   $838.65   $838.70