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 $83.61   11.863%   $93.5287   $93.53   $93.55   $93.50  
  Purchase #2 $240.98   9.790%   $264.5719   $264.57   $264.55   $264.60  
  Purchase #3 $142.99   5.809%   $151.2963   $151.30   $151.30   $151.30  
  Purchase #4 $176.34   11.179%   $196.053   $196.05   $196.05   $196.10  
  Purchase #5 $27.60   9.541%   $30.2333   $30.23   $30.25   $30.20  
  Purchase #6 $195.90   4.557%   $204.8272   $204.83   $204.85   $204.80  
  Purchase #7 $246.42   12.726%   $277.7794   $277.78   $277.80   $277.80  
  7 purchase totals = $1,113.84       $1,218.2898   $1,218.29   $1,218.35   $1,218.30