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 $232.82   4.534%   $243.3761   $243.38   $243.40   $243.40  
  Purchase #2 $166.77   13.111%   $188.6352   $188.64   $188.65   $188.60  
  Purchase #3 $86.55   9.609%   $94.8666   $94.87   $94.85   $94.90  
  Purchase #4 $96.60   8.136%   $104.4594   $104.46   $104.45   $104.50  
  Purchase #5 $94.26   13.780%   $107.249   $107.25   $107.25   $107.20  
  Purchase #6 $55.92   5.231%   $58.8452   $58.85   $58.85   $58.80  
  Purchase #7 $229.68   3.832%   $238.4813   $238.48   $238.50   $238.50  
  7 purchase totals = $962.60       $1,035.9128   $1,035.93   $1,035.95   $1,035.90