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 $175.47   4.835%   $183.954   $183.95   $183.95   $184.00  
  Purchase #2 $44.39   7.423%   $47.6851   $47.69   $47.70   $47.70  
  Purchase #3 $73.51   11.594%   $82.0327   $82.03   $82.05   $82.00  
  Purchase #4 $199.57   9.604%   $218.7367   $218.74   $218.75   $218.70  
  Purchase #5 $230.33   12.437%   $258.9761   $258.98   $259.00   $259.00  
  Purchase #6 $22.36   10.298%   $24.6626   $24.66   $24.65   $24.70  
  Purchase #7 $119.56   3.388%   $123.6107   $123.61   $123.60   $123.60  
  7 purchase totals = $865.19       $939.6579   $939.66   $939.70   $939.70