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 $241.33   3.123%   $248.8667   $248.87   $248.85   $248.90  
  Purchase #2 $229.94   6.222%   $244.2469   $244.25   $244.25   $244.20  
  Purchase #3 $207.31   8.864%   $225.686   $225.69   $225.70   $225.70  
  Purchase #4 $138.25   6.200%   $146.8215   $146.82   $146.80   $146.80  
  Purchase #5 $176.73   8.362%   $191.5082   $191.51   $191.50   $191.50  
  Purchase #6 $28.29   6.383%   $30.0958   $30.10   $30.10   $30.10  
  Purchase #7 $165.96   6.475%   $176.7059   $176.71   $176.70   $176.70  
  7 purchase totals = $1,187.81       $1,263.9310   $1,263.95   $1,263.90   $1,263.90