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 $246.47   11.321%   $274.3729   $274.37   $274.35   $274.40  
  Purchase #2 $61.41   11.607%   $68.5379   $68.54   $68.55   $68.50  
  Purchase #3 $84.65   13.388%   $95.9829   $95.98   $96.00   $96.00  
  Purchase #4 $29.66   3.213%   $30.613   $30.61   $30.60   $30.60  
  Purchase #5 $153.85   4.655%   $161.0117   $161.01   $161.00   $161.00  
  Purchase #6 $62.61   10.463%   $69.1609   $69.16   $69.15   $69.20  
  Purchase #7 $56.53   10.552%   $62.495   $62.50   $62.50   $62.50  
  7 purchase totals = $695.18       $762.1743   $762.17   $762.15   $762.20