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 $62.67   4.761%   $65.6537   $65.65   $65.65   $65.70  
  Purchase #2 $210.38   12.401%   $236.4692   $236.47   $236.45   $236.50  
  Purchase #3 $115.61   9.525%   $126.6219   $126.62   $126.60   $126.60  
  Purchase #4 $141.56   12.593%   $159.3867   $159.39   $159.40   $159.40  
  Purchase #5 $29.36   7.768%   $31.6407   $31.64   $31.65   $31.60  
  Purchase #6 $176.51   9.219%   $192.7825   $192.78   $192.80   $192.80  
  Purchase #7 $203.78   13.759%   $231.8181   $231.82   $231.80   $231.80  
  7 purchase totals = $939.87       $1,044.3728   $1,044.37   $1,044.35   $1,044.40