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 $93.57   5.512%   $98.7276   $98.73   $98.75   $98.70  
  Purchase #2 $168.75   11.279%   $187.7833   $187.78   $187.80   $187.80  
  Purchase #3 $55.57   5.690%   $58.7319   $58.73   $58.75   $58.70  
  Purchase #4 $205.48   6.366%   $218.5609   $218.56   $218.55   $218.60  
  Purchase #5 $25.66   11.425%   $28.5917   $28.59   $28.60   $28.60  
  Purchase #6 $215.55   8.195%   $233.2143   $233.21   $233.20   $233.20  
  Purchase #7 $111.99   3.738%   $116.1762   $116.18   $116.20   $116.20  
  7 purchase totals = $876.57       $941.7859   $941.78   $941.85   $941.80