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 $143.60   6.788%   $153.3476   $153.35   $153.35   $153.30  
  Purchase #2 $178.47   10.807%   $197.7573   $197.76   $197.75   $197.80  
  Purchase #3 $64.53   5.706%   $68.2121   $68.21   $68.20   $68.20  
  Purchase #4 $178.89   12.127%   $200.584   $200.58   $200.60   $200.60  
  Purchase #5 $190.88   11.316%   $212.48   $212.48   $212.50   $212.50  
  Purchase #6 $189.79   13.136%   $214.7208   $214.72   $214.70   $214.70  
  Purchase #7 $232.60   6.511%   $247.7446   $247.74   $247.75   $247.70  
  7 purchase totals = $1,178.76       $1,294.8464   $1,294.84   $1,294.85   $1,294.80