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   8.490%   $249.386   $249.39   $249.40   $249.40  
  Purchase #2 $119.45   5.404%   $125.9051   $125.91   $125.90   $125.90  
  Purchase #3 $120.93   10.528%   $133.6615   $133.66   $133.65   $133.70  
  Purchase #4 $60.38   8.270%   $65.3734   $65.37   $65.35   $65.40  
  Purchase #5 $137.39   7.511%   $147.7094   $147.71   $147.70   $147.70  
  Purchase #6 $25.36   3.614%   $26.2765   $26.28   $26.30   $26.30  
  Purchase #7 $35.30   7.132%   $37.8176   $37.82   $37.80   $37.80  
  7 purchase totals = $728.68       $786.1295   $786.14   $786.10   $786.20