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 $182.92   13.633%   $207.8575   $207.86   $207.85   $207.90  
  Purchase #2 $67.98   10.545%   $75.1485   $75.15   $75.15   $75.10  
  Purchase #3 $66.45   5.111%   $69.8463   $69.85   $69.85   $69.80  
  Purchase #4 $132.88   13.787%   $151.2002   $151.20   $151.20   $151.20  
  Purchase #5 $52.27   6.836%   $55.8432   $55.84   $55.85   $55.80  
  Purchase #6 $203.88   10.548%   $225.3853   $225.39   $225.40   $225.40  
  Purchase #7 $28.97   9.419%   $31.6987   $31.70   $31.70   $31.70  
  7 purchase totals = $735.35       $816.9797   $816.99   $817.00   $816.90