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 $33.63   11.393%   $37.4615   $37.46   $37.45   $37.50  
  Purchase #2 $234.59   12.390%   $263.6557   $263.66   $263.65   $263.70  
  Purchase #3 $42.86   9.640%   $46.9917   $46.99   $47.00   $47.00  
  Purchase #4 $32.93   3.203%   $33.9847   $33.98   $34.00   $34.00  
  Purchase #5 $221.28   6.293%   $235.2052   $235.21   $235.20   $235.20  
  Purchase #6 $89.63   5.406%   $94.4754   $94.48   $94.50   $94.50  
  Purchase #7 $59.72   3.180%   $61.6191   $61.62   $61.60   $61.60  
  7 purchase totals = $714.64       $773.3933   $773.40   $773.40   $773.50