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 $157.51   12.340%   $176.9467   $176.95   $176.95   $176.90  
  Purchase #2 $85.86   11.690%   $95.897   $95.90   $95.90   $95.90  
  Purchase #3 $206.48   9.756%   $226.6242   $226.62   $226.60   $226.60  
  Purchase #4 $248.45   4.871%   $260.552   $260.55   $260.55   $260.60  
  Purchase #5 $41.79   8.449%   $45.3208   $45.32   $45.30   $45.30  
  Purchase #6 $231.38   9.851%   $254.1732   $254.17   $254.15   $254.20  
  Purchase #7 $206.59   3.474%   $213.7669   $213.77   $213.75   $213.80  
  7 purchase totals = $1,178.06       $1,273.2808   $1,273.28   $1,273.20   $1,273.30