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 $46.95   3.609%   $48.6444   $48.64   $48.65   $48.60  
  Purchase #2 $174.46   10.196%   $192.2479   $192.25   $192.25   $192.20  
  Purchase #3 $129.32   13.501%   $146.7795   $146.78   $146.80   $146.80  
  Purchase #4 $5.43   11.340%   $6.0458   $6.05   $6.05   $6.00  
  Purchase #5 $139.50   3.205%   $143.971   $143.97   $143.95   $144.00  
  Purchase #6 $94.59   13.559%   $107.4155   $107.42   $107.40   $107.40  
  Purchase #7 $88.52   5.693%   $93.5594   $93.56   $93.55   $93.60  
  7 purchase totals = $678.77       $738.6635   $738.67   $738.65   $738.60