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 $5.56   8.725%   $6.0451   $6.05   $6.05   $6.00  
  Purchase #2 $238.59   3.148%   $246.1008   $246.10   $246.10   $246.10  
  Purchase #3 $56.90   3.466%   $58.8722   $58.87   $58.85   $58.90  
  Purchase #4 $51.54   9.760%   $56.5703   $56.57   $56.55   $56.60  
  Purchase #5 $175.68   12.309%   $197.3045   $197.30   $197.30   $197.30  
  Purchase #6 $193.57   12.608%   $217.9753   $217.98   $218.00   $218.00  
  Purchase #7 $142.99   8.685%   $155.4087   $155.41   $155.40   $155.40  
  7 purchase totals = $864.83       $938.2769   $938.28   $938.25   $938.30