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 $151.59   11.612%   $169.1926   $169.19   $169.20   $169.20  
  Purchase #2 $220.41   12.348%   $247.6262   $247.63   $247.65   $247.60  
  Purchase #3 $57.90   11.827%   $64.7478   $64.75   $64.75   $64.70  
  Purchase #4 $183.59   5.840%   $194.3117   $194.31   $194.30   $194.30  
  Purchase #5 $64.93   11.353%   $72.3015   $72.30   $72.30   $72.30  
  Purchase #6 $20.40   10.239%   $22.4888   $22.49   $22.50   $22.50  
  Purchase #7 $247.70   6.162%   $262.9633   $262.96   $262.95   $263.00  
  7 purchase totals = $946.52       $1,033.6319   $1,033.63   $1,033.65   $1,033.60