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 $190.61   9.634%   $208.9734   $208.97   $208.95   $209.00  
  Purchase #2 $116.96   8.134%   $126.4735   $126.47   $126.45   $126.50  
  Purchase #3 $249.60   9.399%   $273.0599   $273.06   $273.05   $273.10  
  Purchase #4 $231.80   6.498%   $246.8624   $246.86   $246.85   $246.90  
  Purchase #5 $184.33   7.303%   $197.7916   $197.79   $197.80   $197.80  
  Purchase #6 $59.99   12.224%   $67.3232   $67.32   $67.30   $67.30  
  Purchase #7 $193.29   5.222%   $203.3836   $203.38   $203.40   $203.40  
  7 purchase totals = $1,226.58       $1,323.8676   $1,323.85   $1,323.80   $1,324.00