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 $169.53   13.210%   $191.9249   $191.92   $191.90   $191.90  
  Purchase #2 $241.59   4.153%   $251.6232   $251.62   $251.60   $251.60  
  Purchase #3 $25.97   10.186%   $28.6153   $28.62   $28.60   $28.60  
  Purchase #4 $22.25   13.577%   $25.2709   $25.27   $25.25   $25.30  
  Purchase #5 $13.30   3.721%   $13.7949   $13.79   $13.80   $13.80  
  Purchase #6 $197.41   13.627%   $224.3111   $224.31   $224.30   $224.30  
  Purchase #7 $24.37   5.713%   $25.7623   $25.76   $25.75   $25.80  
  7 purchase totals = $694.42       $761.3026   $761.29   $761.20   $761.30