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 $57.51   5.343%   $60.5828   $60.58   $60.60   $60.60  
  Purchase #2 $50.96   5.469%   $53.747   $53.75   $53.75   $53.70  
  Purchase #3 $184.47   8.448%   $200.054   $200.05   $200.05   $200.10  
  Purchase #4 $102.63   6.611%   $109.4149   $109.41   $109.40   $109.40  
  Purchase #5 $108.26   12.578%   $121.8769   $121.88   $121.90   $121.90  
  Purchase #6 $19.73   10.758%   $21.8526   $21.85   $21.85   $21.90  
  Purchase #7 $182.62   9.269%   $199.547   $199.55   $199.55   $199.50  
  7 purchase totals = $706.18       $767.0752   $767.07   $767.10   $767.10