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 $53.90   11.269%   $59.974   $59.97   $59.95   $60.00  
  Purchase #2 $121.61   9.753%   $133.4706   $133.47   $133.45   $133.50  
  Purchase #3 $195.90   6.515%   $208.6629   $208.66   $208.65   $208.70  
  Purchase #4 $243.26   6.168%   $258.2643   $258.26   $258.25   $258.30  
  Purchase #5 $46.56   9.459%   $50.9641   $50.96   $50.95   $51.00  
  Purchase #6 $32.72   8.816%   $35.6046   $35.60   $35.60   $35.60  
  Purchase #7 $214.48   5.845%   $227.0164   $227.02   $227.00   $227.00  
  7 purchase totals = $908.43       $973.9569   $973.94   $973.85   $974.10