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 $182.32   13.231%   $206.4428   $206.44   $206.45   $206.40  
  Purchase #2 $39.94   3.393%   $41.2952   $41.30   $41.30   $41.30  
  Purchase #3 $58.69   3.438%   $60.7078   $60.71   $60.70   $60.70  
  Purchase #4 $166.93   10.532%   $184.5111   $184.51   $184.50   $184.50  
  Purchase #5 $150.88   10.352%   $166.4991   $166.50   $166.50   $166.50  
  Purchase #6 $40.65   6.175%   $43.1601   $43.16   $43.15   $43.20  
  Purchase #7 $57.59   12.400%   $64.7312   $64.73   $64.75   $64.70  
  7 purchase totals = $697.00       $767.3473   $767.35   $767.35   $767.30