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 $56.47   11.831%   $63.151   $63.15   $63.15   $63.20  
  Purchase #2 $124.33   7.690%   $133.891   $133.89   $133.90   $133.90  
  Purchase #3 $154.34   6.387%   $164.1977   $164.20   $164.20   $164.20  
  Purchase #4 $45.82   10.251%   $50.517   $50.52   $50.50   $50.50  
  Purchase #5 $171.75   3.645%   $178.0103   $178.01   $178.00   $178.00  
  Purchase #6 $171.56   11.792%   $191.7904   $191.79   $191.80   $191.80  
  Purchase #7 $217.94   10.770%   $241.4121   $241.41   $241.40   $241.40  
  7 purchase totals = $942.21       $1,022.9695   $1,022.97   $1,022.95   $1,023.00