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 $117.94   8.201%   $127.6123   $127.61   $127.60   $127.60  
  Purchase #2 $149.40   9.455%   $163.5258   $163.53   $163.55   $163.50  
  Purchase #3 $209.99   8.532%   $227.9063   $227.91   $227.90   $227.90  
  Purchase #4 $241.61   11.698%   $269.8735   $269.87   $269.85   $269.90  
  Purchase #5 $138.60   7.448%   $148.9229   $148.92   $148.90   $148.90  
  Purchase #6 $244.88   13.430%   $277.7674   $277.77   $277.75   $277.80  
  Purchase #7 $144.84   3.142%   $149.3909   $149.39   $149.40   $149.40  
  7 purchase totals = $1,247.26       $1,364.9991   $1,365.00   $1,364.95   $1,365.00