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 $53.36   9.372%   $58.3609   $58.36   $58.35   $58.40  
  Purchase #2 $184.39   10.712%   $204.1419   $204.14   $204.15   $204.10  
  Purchase #3 $70.73   3.853%   $73.4552   $73.46   $73.45   $73.50  
  Purchase #4 $61.98   3.687%   $64.2652   $64.27   $64.25   $64.30  
  Purchase #5 $154.36   4.594%   $161.4513   $161.45   $161.45   $161.50  
  Purchase #6 $239.98   7.467%   $257.8993   $257.90   $257.90   $257.90  
  Purchase #7 $59.55   7.311%   $63.9037   $63.90   $63.90   $63.90  
  7 purchase totals = $824.35       $883.4775   $883.48   $883.45   $883.60