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 $176.28   11.132%   $195.9035   $195.90   $195.90   $195.90  
  Purchase #2 $96.83   5.697%   $102.3464   $102.35   $102.35   $102.30  
  Purchase #3 $95.53   9.356%   $104.4678   $104.47   $104.45   $104.50  
  Purchase #4 $223.84   10.429%   $247.1843   $247.18   $247.20   $247.20  
  Purchase #5 $62.41   10.128%   $68.7309   $68.73   $68.75   $68.70  
  Purchase #6 $94.50   5.505%   $99.7022   $99.70   $99.70   $99.70  
  Purchase #7 $75.76   12.374%   $85.1345   $85.13   $85.15   $85.10  
  7 purchase totals = $825.15       $903.4696   $903.46   $903.50   $903.40