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 $207.59   12.561%   $233.6654   $233.67   $233.65   $233.70  
  Purchase #2 $194.51   3.140%   $200.6176   $200.62   $200.60   $200.60  
  Purchase #3 $99.81   7.485%   $107.2808   $107.28   $107.30   $107.30  
  Purchase #4 $111.70   6.219%   $118.6466   $118.65   $118.65   $118.60  
  Purchase #5 $117.38   11.750%   $131.1722   $131.17   $131.15   $131.20  
  Purchase #6 $52.75   5.707%   $55.7604   $55.76   $55.75   $55.80  
  Purchase #7 $221.73   8.861%   $241.3775   $241.38   $241.40   $241.40  
  7 purchase totals = $1,005.47       $1,088.5205   $1,088.53   $1,088.50   $1,088.60