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 $58.64   5.751%   $62.0124   $62.01   $62.00   $62.00  
  Purchase #2 $166.84   11.206%   $185.5361   $185.54   $185.55   $185.50  
  Purchase #3 $231.46   12.598%   $260.6193   $260.62   $260.60   $260.60  
  Purchase #4 $135.69   11.582%   $151.4056   $151.41   $151.40   $151.40  
  Purchase #5 $157.67   3.260%   $162.81   $162.81   $162.80   $162.80  
  Purchase #6 $44.42   9.770%   $48.7598   $48.76   $48.75   $48.80  
  Purchase #7 $202.87   12.533%   $228.2957   $228.30   $228.30   $228.30  
  7 purchase totals = $997.59       $1,099.4389   $1,099.45   $1,099.40   $1,099.40