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 $239.74   5.587%   $253.1343   $253.13   $253.15   $253.10  
  Purchase #2 $162.39   9.509%   $177.8317   $177.83   $177.85   $177.80  
  Purchase #3 $154.95   8.303%   $167.8155   $167.82   $167.80   $167.80  
  Purchase #4 $202.53   10.776%   $224.3546   $224.35   $224.35   $224.40  
  Purchase #5 $23.71   13.662%   $26.9493   $26.95   $26.95   $26.90  
  Purchase #6 $165.31   10.598%   $182.8296   $182.83   $182.85   $182.80  
  Purchase #7 $59.59   10.648%   $65.9351   $65.94   $65.95   $65.90  
  7 purchase totals = $1,008.22       $1,098.8501   $1,098.85   $1,098.90   $1,098.70