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 $61.51   6.221%   $65.3365   $65.34   $65.35   $65.30  
  Purchase #2 $211.31   10.369%   $233.2207   $233.22   $233.20   $233.20  
  Purchase #3 $6.68   6.651%   $7.1243   $7.12   $7.10   $7.10  
  Purchase #4 $54.66   8.857%   $59.5012   $59.50   $59.50   $59.50  
  Purchase #5 $144.51   9.311%   $157.9653   $157.97   $157.95   $158.00  
  Purchase #6 $13.85   7.432%   $14.8793   $14.88   $14.90   $14.90  
  Purchase #7 $249.93   9.786%   $274.3881   $274.39   $274.40   $274.40  
  7 purchase totals = $742.45       $812.4154   $812.42   $812.40   $812.40