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 $204.66   10.759%   $226.6794   $226.68   $226.70   $226.70  
  Purchase #2 $5.36   11.109%   $5.9554   $5.96   $5.95   $6.00  
  Purchase #3 $130.30   12.236%   $146.2435   $146.24   $146.25   $146.20  
  Purchase #4 $34.61   4.834%   $36.283   $36.28   $36.30   $36.30  
  Purchase #5 $157.32   5.641%   $166.1944   $166.19   $166.20   $166.20  
  Purchase #6 $212.48   5.658%   $224.5021   $224.50   $224.50   $224.50  
  Purchase #7 $229.92   8.290%   $248.9804   $248.98   $249.00   $249.00  
  7 purchase totals = $974.65       $1,054.8382   $1,054.83   $1,054.90   $1,054.90