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 $104.57   8.109%   $113.0496   $113.05   $113.05   $113.00  
  Purchase #2 $200.88   3.209%   $207.3262   $207.33   $207.35   $207.30  
  Purchase #3 $119.65   6.635%   $127.5888   $127.59   $127.60   $127.60  
  Purchase #4 $32.32   5.317%   $34.0385   $34.04   $34.05   $34.00  
  Purchase #5 $11.47   3.401%   $11.8601   $11.86   $11.85   $11.90  
  Purchase #6 $72.76   9.313%   $79.5361   $79.54   $79.55   $79.50  
  Purchase #7 $231.62   12.869%   $261.4272   $261.43   $261.45   $261.40  
  7 purchase totals = $773.27       $834.8265   $834.84   $834.90   $834.70