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 $154.45   8.796%   $168.0354   $168.04   $168.05   $168.00  
  Purchase #2 $105.60   12.542%   $118.8444   $118.84   $118.85   $118.80  
  Purchase #3 $168.29   13.609%   $191.1926   $191.19   $191.20   $191.20  
  Purchase #4 $239.49   7.641%   $257.7894   $257.79   $257.80   $257.80  
  Purchase #5 $172.76   10.287%   $190.5318   $190.53   $190.55   $190.50  
  Purchase #6 $250.55   11.512%   $279.3933   $279.39   $279.40   $279.40  
  Purchase #7 $57.65   4.315%   $60.1376   $60.14   $60.15   $60.10  
  7 purchase totals = $1,148.79       $1,265.9245   $1,265.92   $1,266.00   $1,265.80