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 $62.76   4.235%   $65.4179   $65.42   $65.40   $65.40  
  Purchase #2 $229.57   11.360%   $255.6492   $255.65   $255.65   $255.60  
  Purchase #3 $8.62   5.579%   $9.1009   $9.10   $9.10   $9.10  
  Purchase #4 $131.41   3.758%   $136.3484   $136.35   $136.35   $136.30  
  Purchase #5 $169.68   9.428%   $185.6774   $185.68   $185.70   $185.70  
  Purchase #6 $160.43   3.528%   $166.09   $166.09   $166.10   $166.10  
  Purchase #7 $216.70   13.602%   $246.1755   $246.18   $246.20   $246.20  
  7 purchase totals = $979.17       $1,064.4593   $1,064.47   $1,064.50   $1,064.40