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 $238.73   10.499%   $263.7943   $263.79   $263.80   $263.80  
  Purchase #2 $176.64   9.151%   $192.8043   $192.80   $192.80   $192.80  
  Purchase #3 $154.57   10.258%   $170.4258   $170.43   $170.45   $170.40  
  Purchase #4 $167.92   4.579%   $175.6091   $175.61   $175.60   $175.60  
  Purchase #5 $40.53   9.504%   $44.382   $44.38   $44.40   $44.40  
  Purchase #6 $50.51   4.455%   $52.7602   $52.76   $52.75   $52.80  
  Purchase #7 $56.85   7.696%   $61.2252   $61.23   $61.25   $61.20  
  7 purchase totals = $885.75       $961.0009   $961.00   $961.05   $961.00