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 $44.80   11.324%   $49.8732   $49.87   $49.85   $49.90  
  Purchase #2 $84.44   13.645%   $95.9618   $95.96   $95.95   $96.00  
  Purchase #3 $9.28   8.344%   $10.0543   $10.05   $10.05   $10.10  
  Purchase #4 $41.77   11.142%   $46.424   $46.42   $46.40   $46.40  
  Purchase #5 $235.78   7.501%   $253.4659   $253.47   $253.45   $253.50  
  Purchase #6 $102.75   4.436%   $107.308   $107.31   $107.30   $107.30  
  Purchase #7 $63.50   13.364%   $71.9861   $71.99   $72.00   $72.00  
  7 purchase totals = $582.32       $635.0733   $635.07   $635.00   $635.20