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 $172.49   12.516%   $194.0788   $194.08   $194.10   $194.10  
  Purchase #2 $87.78   8.567%   $95.3001   $95.30   $95.30   $95.30  
  Purchase #3 $212.31   10.629%   $234.8764   $234.88   $234.90   $234.90  
  Purchase #4 $243.90   6.141%   $258.8779   $258.88   $258.90   $258.90  
  Purchase #5 $119.77   4.755%   $125.4651   $125.47   $125.45   $125.50  
  Purchase #6 $169.91   3.494%   $175.8467   $175.85   $175.85   $175.80  
  Purchase #7 $228.47   9.637%   $250.4877   $250.49   $250.50   $250.50  
  7 purchase totals = $1,234.63       $1,334.9327   $1,334.95   $1,335.00   $1,335.00