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 $197.67   5.702%   $208.9411   $208.94   $208.95   $208.90  
  Purchase #2 $32.48   8.666%   $35.2947   $35.29   $35.30   $35.30  
  Purchase #3 $66.54   7.191%   $71.3249   $71.32   $71.30   $71.30  
  Purchase #4 $115.25   3.830%   $119.6641   $119.66   $119.65   $119.70  
  Purchase #5 $28.91   5.163%   $30.4026   $30.40   $30.40   $30.40  
  Purchase #6 $169.66   7.782%   $182.8629   $182.86   $182.85   $182.90  
  Purchase #7 $145.73   7.434%   $156.5636   $156.56   $156.55   $156.60  
  7 purchase totals = $756.24       $805.0539   $805.03   $805.00   $805.10