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 $67.33   13.556%   $76.4573   $76.46   $76.45   $76.50  
  Purchase #2 $244.67   12.361%   $274.9137   $274.91   $274.90   $274.90  
  Purchase #3 $176.40   9.500%   $193.158   $193.16   $193.15   $193.20  
  Purchase #4 $229.75   7.806%   $247.6843   $247.68   $247.70   $247.70  
  Purchase #5 $96.40   6.436%   $102.6043   $102.60   $102.60   $102.60  
  Purchase #6 $209.35   3.395%   $216.4574   $216.46   $216.45   $216.50  
  Purchase #7 $146.57   8.832%   $159.5151   $159.52   $159.50   $159.50  
  7 purchase totals = $1,170.47       $1,270.7901   $1,270.79   $1,270.75   $1,270.90