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 $233.42   3.688%   $242.0285   $242.03   $242.05   $242.00  
  Purchase #2 $197.42   3.170%   $203.6782   $203.68   $203.70   $203.70  
  Purchase #3 $59.38   4.559%   $62.0871   $62.09   $62.10   $62.10  
  Purchase #4 $223.49   7.283%   $239.7668   $239.77   $239.75   $239.80  
  Purchase #5 $232.79   4.832%   $244.0384   $244.04   $244.05   $244.00  
  Purchase #6 $236.71   10.173%   $260.7905   $260.79   $260.80   $260.80  
  Purchase #7 $223.66   10.329%   $246.7618   $246.76   $246.75   $246.80  
  7 purchase totals = $1,406.87       $1,499.1513   $1,499.16   $1,499.20   $1,499.20