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 $44.67   11.827%   $49.9531   $49.95   $49.95   $50.00  
  Purchase #2 $33.47   9.791%   $36.747   $36.75   $36.75   $36.70  
  Purchase #3 $43.73   13.536%   $49.6493   $49.65   $49.65   $49.60  
  Purchase #4 $229.93   6.867%   $245.7193   $245.72   $245.70   $245.70  
  Purchase #5 $123.94   8.176%   $134.0733   $134.07   $134.05   $134.10  
  Purchase #6 $182.45   10.855%   $202.2549   $202.25   $202.25   $202.30  
  Purchase #7 $171.30   4.800%   $179.5224   $179.52   $179.50   $179.50  
  7 purchase totals = $829.49       $897.9193   $897.91   $897.85   $897.90