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 $209.78   12.321%   $235.627   $235.63   $235.65   $235.60  
  Purchase #2 $109.69   11.455%   $122.255   $122.26   $122.25   $122.30  
  Purchase #3 $236.48   13.178%   $267.6433   $267.64   $267.65   $267.60  
  Purchase #4 $112.66   6.290%   $119.7463   $119.75   $119.75   $119.70  
  Purchase #5 $79.51   10.793%   $88.0915   $88.09   $88.10   $88.10  
  Purchase #6 $246.97   6.279%   $262.4772   $262.48   $262.50   $262.50  
  Purchase #7 $234.86   12.580%   $264.4054   $264.41   $264.40   $264.40  
  7 purchase totals = $1,229.95       $1,360.2457   $1,360.26   $1,360.30   $1,360.20