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 $195.30   13.252%   $221.1812   $221.18   $221.20   $221.20  
  Purchase #2 $204.89   9.156%   $223.6497   $223.65   $223.65   $223.60  
  Purchase #3 $63.57   10.496%   $70.2423   $70.24   $70.25   $70.20  
  Purchase #4 $123.91   6.837%   $132.3817   $132.38   $132.40   $132.40  
  Purchase #5 $89.55   6.817%   $95.6546   $95.65   $95.65   $95.70  
  Purchase #6 $237.37   10.352%   $261.9425   $261.94   $261.95   $261.90  
  Purchase #7 $145.42   11.602%   $162.2916   $162.29   $162.30   $162.30  
  7 purchase totals = $1,060.01       $1,167.3436   $1,167.33   $1,167.40   $1,167.30