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 $180.54   7.454%   $193.9975   $194.00   $194.00   $194.00  
  Purchase #2 $6.42   7.121%   $6.8772   $6.88   $6.90   $6.90  
  Purchase #3 $59.64   6.358%   $63.4319   $63.43   $63.45   $63.40  
  Purchase #4 $208.73   4.658%   $218.4526   $218.45   $218.45   $218.50  
  Purchase #5 $141.95   7.798%   $153.0193   $153.02   $153.00   $153.00  
  Purchase #6 $117.74   13.803%   $133.9917   $133.99   $134.00   $134.00  
  Purchase #7 $79.92   5.487%   $84.3052   $84.31   $84.30   $84.30  
  7 purchase totals = $794.94       $854.0754   $854.08   $854.10   $854.10