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 $169.85   9.382%   $185.7853   $185.79   $185.80   $185.80  
  Purchase #2 $161.25   13.466%   $182.9639   $182.96   $182.95   $183.00  
  Purchase #3 $25.38   3.199%   $26.1919   $26.19   $26.20   $26.20  
  Purchase #4 $180.98   4.742%   $189.5621   $189.56   $189.55   $189.60  
  Purchase #5 $56.70   8.695%   $61.6301   $61.63   $61.65   $61.60  
  Purchase #6 $124.63   10.220%   $137.3672   $137.37   $137.35   $137.40  
  Purchase #7 $160.36   5.651%   $169.4219   $169.42   $169.40   $169.40  
  7 purchase totals = $879.15       $952.9224   $952.92   $952.90   $953.00