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 $106.59   6.620%   $113.6463   $113.65   $113.65   $113.60  
  Purchase #2 $128.97   11.379%   $143.6455   $143.65   $143.65   $143.60  
  Purchase #3 $32.30   6.822%   $34.5035   $34.50   $34.50   $34.50  
  Purchase #4 $154.44   7.407%   $165.8794   $165.88   $165.90   $165.90  
  Purchase #5 $98.95   8.719%   $107.5775   $107.58   $107.60   $107.60  
  Purchase #6 $19.70   5.377%   $20.7593   $20.76   $20.75   $20.80  
  Purchase #7 $172.31   9.498%   $188.676   $188.68   $188.70   $188.70  
  7 purchase totals = $713.26       $774.6875   $774.70   $774.75   $774.70