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 $246.52   11.257%   $274.2708   $274.27   $274.25   $274.30  
  Purchase #2 $12.80   13.759%   $14.5612   $14.56   $14.55   $14.60  
  Purchase #3 $147.76   6.807%   $157.818   $157.82   $157.80   $157.80  
  Purchase #4 $32.68   5.425%   $34.4529   $34.45   $34.45   $34.50  
  Purchase #5 $97.49   7.336%   $104.6419   $104.64   $104.65   $104.60  
  Purchase #6 $66.59   10.682%   $73.7031   $73.70   $73.70   $73.70  
  Purchase #7 $96.28   3.471%   $99.6219   $99.62   $99.60   $99.60  
  7 purchase totals = $700.12       $759.0698   $759.06   $759.00   $759.10