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 $195.37   6.264%   $207.608   $207.61   $207.60   $207.60  
  Purchase #2 $166.77   6.114%   $176.9663   $176.97   $176.95   $177.00  
  Purchase #3 $140.57   11.661%   $156.9619   $156.96   $156.95   $157.00  
  Purchase #4 $89.31   7.322%   $95.8493   $95.85   $95.85   $95.80  
  Purchase #5 $49.74   8.436%   $53.9361   $53.94   $53.95   $53.90  
  Purchase #6 $208.75   13.485%   $236.8999   $236.90   $236.90   $236.90  
  Purchase #7 $13.66   4.841%   $14.3213   $14.32   $14.30   $14.30  
  7 purchase totals = $864.17       $942.5428   $942.55   $942.50   $942.50