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 $59.35   9.489%   $64.9817   $64.98   $65.00   $65.00  
  Purchase #2 $41.49   10.249%   $45.7423   $45.74   $45.75   $45.70  
  Purchase #3 $238.60   4.237%   $248.7095   $248.71   $248.70   $248.70  
  Purchase #4 $97.76   13.748%   $111.2   $111.20   $111.20   $111.20  
  Purchase #5 $132.60   6.772%   $141.5797   $141.58   $141.60   $141.60  
  Purchase #6 $22.42   12.543%   $25.2321   $25.23   $25.25   $25.20  
  Purchase #7 $156.66   12.761%   $176.6514   $176.65   $176.65   $176.70  
  7 purchase totals = $748.88       $814.0967   $814.09   $814.15   $814.10