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 $70.31   4.212%   $73.2715   $73.27   $73.25   $73.30  
  Purchase #2 $230.93   10.256%   $254.6142   $254.61   $254.60   $254.60  
  Purchase #3 $122.62   9.561%   $134.3437   $134.34   $134.35   $134.30  
  Purchase #4 $168.46   8.237%   $182.3361   $182.34   $182.35   $182.30  
  Purchase #5 $180.86   13.748%   $205.7246   $205.72   $205.70   $205.70  
  Purchase #6 $54.79   10.626%   $60.612   $60.61   $60.60   $60.60  
  Purchase #7 $30.36   7.529%   $32.6458   $32.65   $32.65   $32.60  
  7 purchase totals = $858.33       $943.5479   $943.54   $943.50   $943.40