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 $85.99   11.616%   $95.9786   $95.98   $96.00   $96.00  
  Purchase #2 $56.72   11.809%   $63.4181   $63.42   $63.40   $63.40  
  Purchase #3 $155.83   9.409%   $170.492   $170.49   $170.50   $170.50  
  Purchase #4 $51.67   6.556%   $55.0575   $55.06   $55.05   $55.10  
  Purchase #5 $33.38   9.759%   $36.6376   $36.64   $36.65   $36.60  
  Purchase #6 $202.54   11.283%   $225.3926   $225.39   $225.40   $225.40  
  Purchase #7 $174.78   3.301%   $180.5495   $180.55   $180.55   $180.50  
  7 purchase totals = $760.91       $827.5259   $827.53   $827.55   $827.50