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 $73.25   13.456%   $83.1065   $83.11   $83.10   $83.10  
  Purchase #2 $178.78   7.702%   $192.5496   $192.55   $192.55   $192.50  
  Purchase #3 $13.98   5.817%   $14.7932   $14.79   $14.80   $14.80  
  Purchase #4 $13.85   5.346%   $14.5904   $14.59   $14.60   $14.60  
  Purchase #5 $208.72   3.784%   $216.618   $216.62   $216.60   $216.60  
  Purchase #6 $195.61   12.472%   $220.0065   $220.01   $220.00   $220.00  
  Purchase #7 $63.66   4.864%   $66.7564   $66.76   $66.75   $66.80  
  7 purchase totals = $747.85       $808.4206   $808.43   $808.40   $808.40