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 $233.40   12.618%   $262.8504   $262.85   $262.85   $262.90  
  Purchase #2 $91.91   10.384%   $101.4539   $101.45   $101.45   $101.50  
  Purchase #3 $69.32   5.344%   $73.0245   $73.02   $73.00   $73.00  
  Purchase #4 $204.92   9.413%   $224.2091   $224.21   $224.20   $224.20  
  Purchase #5 $118.37   5.626%   $125.0295   $125.03   $125.05   $125.00  
  Purchase #6 $79.71   13.546%   $90.5075   $90.51   $90.50   $90.50  
  Purchase #7 $65.57   12.158%   $73.542   $73.54   $73.55   $73.50  
  7 purchase totals = $863.20       $950.6169   $950.61   $950.60   $950.60