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 $59.77   6.476%   $63.6407   $63.64   $63.65   $63.60  
  Purchase #2 $131.29   4.389%   $137.0523   $137.05   $137.05   $137.10  
  Purchase #3 $242.43   8.293%   $262.5347   $262.53   $262.55   $262.50  
  Purchase #4 $77.79   5.314%   $81.9238   $81.92   $81.90   $81.90  
  Purchase #5 $69.25   7.575%   $74.4957   $74.50   $74.50   $74.50  
  Purchase #6 $230.65   4.309%   $240.5887   $240.59   $240.60   $240.60  
  Purchase #7 $72.42   4.658%   $75.7933   $75.79   $75.80   $75.80  
  7 purchase totals = $883.60       $936.0292   $936.02   $936.05   $936.00