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 $101.59   6.122%   $107.8093   $107.81   $107.80   $107.80  
  Purchase #2 $104.74   12.226%   $117.5455   $117.55   $117.55   $117.50  
  Purchase #3 $218.63   10.303%   $241.1554   $241.16   $241.15   $241.20  
  Purchase #4 $205.81   10.169%   $226.7388   $226.74   $226.75   $226.70  
  Purchase #5 $109.72   6.707%   $117.0789   $117.08   $117.10   $117.10  
  Purchase #6 $40.42   11.827%   $45.2005   $45.20   $45.20   $45.20  
  Purchase #7 $130.26   8.722%   $141.6213   $141.62   $141.60   $141.60  
  7 purchase totals = $911.17       $997.1497   $997.16   $997.15   $997.10