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 $214.69   9.336%   $234.7335   $234.73   $234.75   $234.70  
  Purchase #2 $209.77   5.652%   $221.6262   $221.63   $221.65   $221.60  
  Purchase #3 $98.65   13.161%   $111.6333   $111.63   $111.65   $111.60  
  Purchase #4 $101.39   13.607%   $115.1861   $115.19   $115.20   $115.20  
  Purchase #5 $26.32   11.866%   $29.4431   $29.44   $29.45   $29.40  
  Purchase #6 $235.45   10.178%   $259.4141   $259.41   $259.40   $259.40  
  Purchase #7 $197.74   8.449%   $214.4471   $214.45   $214.45   $214.40  
  7 purchase totals = $1,084.01       $1,186.4834   $1,186.48   $1,186.55   $1,186.30