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 $159.96   10.193%   $176.2647   $176.26   $176.25   $176.30  
  Purchase #2 $155.72   6.785%   $166.2856   $166.29   $166.30   $166.30  
  Purchase #3 $211.88   11.862%   $237.0132   $237.01   $237.00   $237.00  
  Purchase #4 $171.35   3.759%   $177.791   $177.79   $177.80   $177.80  
  Purchase #5 $72.93   4.515%   $76.2228   $76.22   $76.20   $76.20  
  Purchase #6 $222.92   11.113%   $247.6931   $247.69   $247.70   $247.70  
  Purchase #7 $159.83   13.542%   $181.4742   $181.47   $181.45   $181.50  
  7 purchase totals = $1,154.59       $1,262.7446   $1,262.73   $1,262.70   $1,262.80