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 $91.25   10.842%   $101.1433   $101.14   $101.15   $101.10  
  Purchase #2 $173.82   12.686%   $195.8708   $195.87   $195.85   $195.90  
  Purchase #3 $205.69   4.482%   $214.909   $214.91   $214.90   $214.90  
  Purchase #4 $179.37   13.810%   $204.141   $204.14   $204.15   $204.10  
  Purchase #5 $187.63   12.296%   $210.701   $210.70   $210.70   $210.70  
  Purchase #6 $192.73   4.818%   $202.0157   $202.02   $202.00   $202.00  
  Purchase #7 $79.58   6.225%   $84.5339   $84.53   $84.55   $84.50  
  7 purchase totals = $1,110.07       $1,213.3147   $1,213.31   $1,213.30   $1,213.20