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 $59.33   5.483%   $62.5831   $62.58   $62.60   $62.60  
  Purchase #2 $123.83   5.207%   $130.2778   $130.28   $130.30   $130.30  
  Purchase #3 $141.95   13.702%   $161.4   $161.40   $161.40   $161.40  
  Purchase #4 $58.68   7.282%   $62.9531   $62.95   $62.95   $63.00  
  Purchase #5 $143.67   3.150%   $148.1956   $148.20   $148.20   $148.20  
  Purchase #6 $67.91   8.334%   $73.5696   $73.57   $73.55   $73.60  
  Purchase #7 $128.53   12.607%   $144.7338   $144.73   $144.75   $144.70  
  7 purchase totals = $723.90       $783.7130   $783.71   $783.75   $783.80