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 $166.28   5.213%   $174.9482   $174.95   $174.95   $174.90  
  Purchase #2 $97.79   5.171%   $102.8467   $102.85   $102.85   $102.80  
  Purchase #3 $90.88   11.375%   $101.2176   $101.22   $101.20   $101.20  
  Purchase #4 $59.36   11.806%   $66.368   $66.37   $66.35   $66.40  
  Purchase #5 $84.75   10.114%   $93.3216   $93.32   $93.30   $93.30  
  Purchase #6 $187.40   9.151%   $204.549   $204.55   $204.55   $204.50  
  Purchase #7 $73.88   9.138%   $80.6312   $80.63   $80.65   $80.60  
  7 purchase totals = $760.34       $823.8823   $823.89   $823.85   $823.70