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 $204.39   5.322%   $215.2676   $215.27   $215.25   $215.30  
  Purchase #2 $124.74   7.662%   $134.2976   $134.30   $134.30   $134.30  
  Purchase #3 $224.68   13.481%   $254.9691   $254.97   $254.95   $255.00  
  Purchase #4 $103.33   10.127%   $113.7942   $113.79   $113.80   $113.80  
  Purchase #5 $41.33   5.456%   $43.585   $43.59   $43.60   $43.60  
  Purchase #6 $59.28   9.344%   $64.8191   $64.82   $64.80   $64.80  
  Purchase #7 $67.89   12.367%   $76.286   $76.29   $76.30   $76.30  
  7 purchase totals = $825.64       $903.0186   $903.03   $903.00   $903.10