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 $148.91   6.567%   $158.6889   $158.69   $158.70   $158.70  
  Purchase #2 $247.72   13.713%   $281.6898   $281.69   $281.70   $281.70  
  Purchase #3 $61.70   12.731%   $69.555   $69.56   $69.55   $69.60  
  Purchase #4 $250.47   3.488%   $259.2064   $259.21   $259.20   $259.20  
  Purchase #5 $60.65   3.591%   $62.8279   $62.83   $62.85   $62.80  
  Purchase #6 $166.57   4.577%   $174.1939   $174.19   $174.20   $174.20  
  Purchase #7 $20.40   5.395%   $21.5006   $21.50   $21.50   $21.50  
  7 purchase totals = $956.42       $1,027.6625   $1,027.67   $1,027.70   $1,027.70