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 $53.40   13.816%   $60.7777   $60.78   $60.80   $60.80  
  Purchase #2 $243.85   5.263%   $256.6838   $256.68   $256.70   $256.70  
  Purchase #3 $62.51   10.826%   $69.2773   $69.28   $69.30   $69.30  
  Purchase #4 $199.74   5.459%   $210.6438   $210.64   $210.65   $210.60  
  Purchase #5 $110.52   4.866%   $115.8979   $115.90   $115.90   $115.90  
  Purchase #6 $214.28   9.188%   $233.968   $233.97   $233.95   $234.00  
  Purchase #7 $17.49   5.234%   $18.4054   $18.41   $18.40   $18.40  
  7 purchase totals = $901.79       $965.6539   $965.66   $965.70   $965.70