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 $229.87   13.682%   $261.3208   $261.32   $261.30   $261.30  
  Purchase #2 $177.88   5.219%   $187.1636   $187.16   $187.15   $187.20  
  Purchase #3 $73.76   11.276%   $82.0772   $82.08   $82.10   $82.10  
  Purchase #4 $163.91   12.850%   $184.9724   $184.97   $184.95   $185.00  
  Purchase #5 $14.57   13.435%   $16.5275   $16.53   $16.55   $16.50  
  Purchase #6 $44.54   11.286%   $49.5668   $49.57   $49.55   $49.60  
  Purchase #7 $216.45   11.268%   $240.8396   $240.84   $240.85   $240.80  
  7 purchase totals = $920.98       $1,022.4679   $1,022.47   $1,022.45   $1,022.50