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 $118.73   4.695%   $124.3044   $124.30   $124.30   $124.30  
  Purchase #2 $153.70   8.574%   $166.8782   $166.88   $166.90   $166.90  
  Purchase #3 $146.75   12.169%   $164.608   $164.61   $164.60   $164.60  
  Purchase #4 $36.46   13.795%   $41.4897   $41.49   $41.50   $41.50  
  Purchase #5 $242.91   10.322%   $267.9832   $267.98   $268.00   $268.00  
  Purchase #6 $49.71   6.534%   $52.9581   $52.96   $52.95   $53.00  
  Purchase #7 $220.47   11.536%   $245.9034   $245.90   $245.90   $245.90  
  7 purchase totals = $968.73       $1,064.1250   $1,064.12   $1,064.15   $1,064.20