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 $128.73   13.422%   $146.0081   $146.01   $146.00   $146.00  
  Purchase #2 $165.45   10.528%   $182.8686   $182.87   $182.85   $182.90  
  Purchase #3 $62.85   13.178%   $71.1324   $71.13   $71.15   $71.10  
  Purchase #4 $95.47   12.553%   $107.4543   $107.45   $107.45   $107.50  
  Purchase #5 $61.43   7.288%   $65.907   $65.91   $65.90   $65.90  
  Purchase #6 $216.46   7.596%   $232.9023   $232.90   $232.90   $232.90  
  Purchase #7 $39.66   8.444%   $43.0089   $43.01   $43.00   $43.00  
  7 purchase totals = $770.05       $849.2816   $849.28   $849.25   $849.30