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 $47.86   12.551%   $53.8669   $53.87   $53.85   $53.90  
  Purchase #2 $207.53   11.304%   $230.9892   $230.99   $231.00   $231.00  
  Purchase #3 $10.96   5.557%   $11.569   $11.57   $11.55   $11.60  
  Purchase #4 $61.92   9.559%   $67.8389   $67.84   $67.85   $67.80  
  Purchase #5 $108.82   8.661%   $118.2449   $118.24   $118.25   $118.20  
  Purchase #6 $123.57   13.547%   $140.31   $140.31   $140.30   $140.30  
  Purchase #7 $131.40   11.161%   $146.0656   $146.07   $146.05   $146.10  
  7 purchase totals = $692.06       $768.8845   $768.89   $768.85   $768.90