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 $202.69   10.634%   $224.2441   $224.24   $224.25   $224.20  
  Purchase #2 $227.86   5.633%   $240.6954   $240.70   $240.70   $240.70  
  Purchase #3 $118.72   12.729%   $133.8319   $133.83   $133.85   $133.80  
  Purchase #4 $85.25   13.754%   $96.9753   $96.98   $97.00   $97.00  
  Purchase #5 $13.69   4.855%   $14.3546   $14.35   $14.35   $14.40  
  Purchase #6 $234.49   11.655%   $261.8198   $261.82   $261.80   $261.80  
  Purchase #7 $109.68   7.762%   $118.1934   $118.19   $118.20   $118.20  
  7 purchase totals = $992.38       $1,090.1145   $1,090.11   $1,090.15   $1,090.10