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 $184.83   12.682%   $208.2701   $208.27   $208.25   $208.30  
  Purchase #2 $141.52   7.224%   $151.7434   $151.74   $151.75   $151.70  
  Purchase #3 $250.30   9.854%   $274.9646   $274.96   $274.95   $275.00  
  Purchase #4 $84.56   13.750%   $96.187   $96.19   $96.20   $96.20  
  Purchase #5 $75.58   12.134%   $84.7509   $84.75   $84.75   $84.80  
  Purchase #6 $151.51   13.277%   $171.626   $171.63   $171.65   $171.60  
  Purchase #7 $56.27   8.826%   $61.2364   $61.24   $61.25   $61.20  
  7 purchase totals = $944.57       $1,048.7784   $1,048.78   $1,048.80   $1,048.80