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 $62.61   10.244%   $69.0238   $69.02   $69.00   $69.00  
  Purchase #2 $165.84   12.161%   $186.0078   $186.01   $186.00   $186.00  
  Purchase #3 $187.32   11.697%   $209.2308   $209.23   $209.25   $209.20  
  Purchase #4 $62.68   10.391%   $69.1931   $69.19   $69.20   $69.20  
  Purchase #5 $60.93   12.845%   $68.7565   $68.76   $68.75   $68.80  
  Purchase #6 $219.79   6.256%   $233.5401   $233.54   $233.55   $233.50  
  Purchase #7 $42.58   12.429%   $47.8723   $47.87   $47.85   $47.90  
  7 purchase totals = $801.75       $883.6244   $883.62   $883.60   $883.60