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 $111.95   12.267%   $125.6829   $125.68   $125.70   $125.70  
  Purchase #2 $147.52   7.333%   $158.3376   $158.34   $158.35   $158.30  
  Purchase #3 $234.72   4.284%   $244.7754   $244.78   $244.80   $244.80  
  Purchase #4 $59.29   9.332%   $64.8229   $64.82   $64.80   $64.80  
  Purchase #5 $153.35   3.124%   $158.1407   $158.14   $158.15   $158.10  
  Purchase #6 $171.92   7.579%   $184.9498   $184.95   $184.95   $184.90  
  Purchase #7 $105.73   9.680%   $115.9647   $115.96   $115.95   $116.00  
  7 purchase totals = $984.48       $1,052.6740   $1,052.67   $1,052.70   $1,052.60