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 $48.41   12.244%   $54.3373   $54.34   $54.35   $54.30  
  Purchase #2 $54.28   11.742%   $60.6536   $60.65   $60.65   $60.70  
  Purchase #3 $52.55   12.709%   $59.2286   $59.23   $59.25   $59.20  
  Purchase #4 $229.99   10.707%   $254.615   $254.62   $254.60   $254.60  
  Purchase #5 $101.61   13.365%   $115.1902   $115.19   $115.20   $115.20  
  Purchase #6 $153.36   4.516%   $160.2857   $160.29   $160.30   $160.30  
  Purchase #7 $247.87   7.637%   $266.7998   $266.80   $266.80   $266.80  
  7 purchase totals = $888.07       $971.1102   $971.12   $971.15   $971.10