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 $143.44   6.692%   $153.039   $153.04   $153.05   $153.00  
  Purchase #2 $196.88   12.565%   $221.618   $221.62   $221.60   $221.60  
  Purchase #3 $40.42   3.429%   $41.806   $41.81   $41.80   $41.80  
  Purchase #4 $95.98   12.125%   $107.6176   $107.62   $107.60   $107.60  
  Purchase #5 $22.32   11.538%   $24.8953   $24.90   $24.90   $24.90  
  Purchase #6 $239.85   13.102%   $271.2751   $271.28   $271.30   $271.30  
  Purchase #7 $215.87   13.425%   $244.8505   $244.85   $244.85   $244.90  
  7 purchase totals = $954.76       $1,065.1015   $1,065.12   $1,065.10   $1,065.10