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 $183.86   6.611%   $196.015   $196.02   $196.00   $196.00  
  Purchase #2 $185.63   9.855%   $203.9238   $203.92   $203.90   $203.90  
  Purchase #3 $9.71   12.735%   $10.9466   $10.95   $10.95   $10.90  
  Purchase #4 $75.96   4.807%   $79.6114   $79.61   $79.60   $79.60  
  Purchase #5 $126.73   11.498%   $141.3014   $141.30   $141.30   $141.30  
  Purchase #6 $191.27   13.504%   $217.0991   $217.10   $217.10   $217.10  
  Purchase #7 $224.86   10.267%   $247.9464   $247.95   $247.95   $247.90  
  7 purchase totals = $998.02       $1,096.8437   $1,096.85   $1,096.80   $1,096.70