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 $95.27   8.526%   $103.3927   $103.39   $103.40   $103.40  
  Purchase #2 $60.70   12.279%   $68.1534   $68.15   $68.15   $68.20  
  Purchase #3 $216.63   10.145%   $238.6071   $238.61   $238.60   $238.60  
  Purchase #4 $162.26   12.527%   $182.5863   $182.59   $182.60   $182.60  
  Purchase #5 $183.61   6.194%   $194.9828   $194.98   $195.00   $195.00  
  Purchase #6 $240.74   5.217%   $253.2994   $253.30   $253.30   $253.30  
  Purchase #7 $99.38   11.425%   $110.7342   $110.73   $110.75   $110.70  
  7 purchase totals = $1,058.59       $1,151.7559   $1,151.75   $1,151.80   $1,151.80