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 $246.97   6.168%   $262.2031   $262.20   $262.20   $262.20  
  Purchase #2 $187.77   4.869%   $196.9125   $196.91   $196.90   $196.90  
  Purchase #3 $38.37   9.185%   $41.8943   $41.89   $41.90   $41.90  
  Purchase #4 $75.95   6.482%   $80.8731   $80.87   $80.85   $80.90  
  Purchase #5 $113.70   10.859%   $126.0467   $126.05   $126.05   $126.00  
  Purchase #6 $34.32   5.768%   $36.2996   $36.30   $36.30   $36.30  
  Purchase #7 $33.66   12.825%   $37.9769   $37.98   $38.00   $38.00  
  7 purchase totals = $730.74       $782.2062   $782.20   $782.20   $782.20