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 $88.98   8.239%   $96.3111   $96.31   $96.30   $96.30  
  Purchase #2 $174.36   5.303%   $183.6063   $183.61   $183.60   $183.60  
  Purchase #3 $123.86   10.581%   $136.9656   $136.97   $136.95   $137.00  
  Purchase #4 $45.56   4.819%   $47.7555   $47.76   $47.75   $47.80  
  Purchase #5 $79.66   11.489%   $88.8121   $88.81   $88.80   $88.80  
  Purchase #6 $27.75   8.681%   $30.159   $30.16   $30.15   $30.20  
  Purchase #7 $223.36   4.187%   $232.7121   $232.71   $232.70   $232.70  
  7 purchase totals = $763.53       $816.3217   $816.33   $816.25   $816.40