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 $213.97   11.700%   $239.0045   $239.00   $239.00   $239.00  
  Purchase #2 $246.73   12.289%   $277.0506   $277.05   $277.05   $277.10  
  Purchase #3 $65.98   11.194%   $73.3658   $73.37   $73.35   $73.40  
  Purchase #4 $166.63   11.413%   $185.6475   $185.65   $185.65   $185.60  
  Purchase #5 $77.37   10.840%   $85.7569   $85.76   $85.75   $85.80  
  Purchase #6 $117.97   4.732%   $123.5523   $123.55   $123.55   $123.60  
  Purchase #7 $184.92   5.468%   $195.0314   $195.03   $195.05   $195.00  
  7 purchase totals = $1,073.57       $1,179.4090   $1,179.41   $1,179.40   $1,179.50