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 $123.87   5.444%   $130.6135   $130.61   $130.60   $130.60  
  Purchase #2 $94.43   6.449%   $100.5198   $100.52   $100.50   $100.50  
  Purchase #3 $79.73   8.700%   $86.6665   $86.67   $86.65   $86.70  
  Purchase #4 $32.68   3.472%   $33.8146   $33.81   $33.80   $33.80  
  Purchase #5 $186.56   12.430%   $209.7494   $209.75   $209.75   $209.70  
  Purchase #6 $66.63   4.337%   $69.5197   $69.52   $69.50   $69.50  
  Purchase #7 $229.62   12.271%   $257.7967   $257.80   $257.80   $257.80  
  7 purchase totals = $813.52       $888.6802   $888.68   $888.60   $888.60