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 $54.81   3.241%   $56.5864   $56.59   $56.60   $56.60  
  Purchase #2 $205.27   11.466%   $228.8063   $228.81   $228.80   $228.80  
  Purchase #3 $224.34   4.548%   $234.543   $234.54   $234.55   $234.50  
  Purchase #4 $105.64   9.302%   $115.4666   $115.47   $115.45   $115.50  
  Purchase #5 $125.78   7.645%   $135.3959   $135.40   $135.40   $135.40  
  Purchase #6 $44.31   7.674%   $47.7103   $47.71   $47.70   $47.70  
  Purchase #7 $194.64   11.247%   $216.5312   $216.53   $216.55   $216.50  
  7 purchase totals = $954.79       $1,035.0397   $1,035.05   $1,035.05   $1,035.00