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 $169.95   13.338%   $192.6179   $192.62   $192.60   $192.60  
  Purchase #2 $131.72   6.137%   $139.8037   $139.80   $139.80   $139.80  
  Purchase #3 $164.79   6.577%   $175.6282   $175.63   $175.65   $175.60  
  Purchase #4 $231.26   4.421%   $241.484   $241.48   $241.50   $241.50  
  Purchase #5 $111.96   3.250%   $115.5987   $115.60   $115.60   $115.60  
  Purchase #6 $191.92   9.521%   $210.1927   $210.19   $210.20   $210.20  
  Purchase #7 $175.75   12.404%   $197.55   $197.55   $197.55   $197.60  
  7 purchase totals = $1,177.35       $1,272.8752   $1,272.87   $1,272.90   $1,272.90