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 $162.75   8.590%   $176.7302   $176.73   $176.75   $176.70  
  Purchase #2 $52.51   4.565%   $54.9071   $54.91   $54.90   $54.90  
  Purchase #3 $65.39   11.238%   $72.7385   $72.74   $72.75   $72.70  
  Purchase #4 $140.87   5.577%   $148.7263   $148.73   $148.75   $148.70  
  Purchase #5 $198.63   8.118%   $214.7548   $214.75   $214.75   $214.80  
  Purchase #6 $175.33   3.131%   $180.8196   $180.82   $180.80   $180.80  
  Purchase #7 $95.81   6.410%   $101.9514   $101.95   $101.95   $102.00  
  7 purchase totals = $891.29       $950.6279   $950.63   $950.65   $950.60