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 $247.63   9.761%   $271.8012   $271.80   $271.80   $271.80  
  Purchase #2 $96.71   7.476%   $103.94   $103.94   $103.95   $103.90  
  Purchase #3 $27.55   3.321%   $28.4649   $28.46   $28.45   $28.50  
  Purchase #4 $107.95   13.162%   $122.1584   $122.16   $122.15   $122.20  
  Purchase #5 $170.45   8.197%   $184.4218   $184.42   $184.40   $184.40  
  Purchase #6 $119.70   5.458%   $126.2332   $126.23   $126.25   $126.20  
  Purchase #7 $216.96   12.313%   $243.6743   $243.67   $243.65   $243.70  
  7 purchase totals = $986.95       $1,080.6938   $1,080.68   $1,080.65   $1,080.70