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 $42.91   7.259%   $46.0248   $46.02   $46.00   $46.00  
  Purchase #2 $211.39   10.683%   $233.9728   $233.97   $233.95   $234.00  
  Purchase #3 $228.46   8.474%   $247.8197   $247.82   $247.80   $247.80  
  Purchase #4 $206.95   13.755%   $235.416   $235.42   $235.40   $235.40  
  Purchase #5 $5.43   10.465%   $5.9982   $6.00   $6.00   $6.00  
  Purchase #6 $71.35   5.656%   $75.3856   $75.39   $75.40   $75.40  
  Purchase #7 $86.84   4.403%   $90.6636   $90.66   $90.65   $90.70  
  7 purchase totals = $853.33       $935.2807   $935.28   $935.20   $935.30