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 $178.63   8.131%   $193.1544   $193.15   $193.15   $193.20  
  Purchase #2 $55.39   9.501%   $60.6526   $60.65   $60.65   $60.70  
  Purchase #3 $168.41   8.775%   $183.188   $183.19   $183.20   $183.20  
  Purchase #4 $43.82   12.209%   $49.17   $49.17   $49.15   $49.20  
  Purchase #5 $187.48   6.365%   $199.4131   $199.41   $199.40   $199.40  
  Purchase #6 $86.37   4.394%   $90.1651   $90.17   $90.15   $90.20  
  Purchase #7 $159.98   9.432%   $175.0693   $175.07   $175.05   $175.10  
  7 purchase totals = $880.08       $950.8125   $950.81   $950.75   $951.00