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 $66.97   3.582%   $69.3689   $69.37   $69.35   $69.40  
  Purchase #2 $182.36   3.466%   $188.6806   $188.68   $188.70   $188.70  
  Purchase #3 $96.44   5.205%   $101.4597   $101.46   $101.45   $101.50  
  Purchase #4 $241.51   7.326%   $259.203   $259.20   $259.20   $259.20  
  Purchase #5 $58.42   5.108%   $61.4041   $61.40   $61.40   $61.40  
  Purchase #6 $135.60   13.643%   $154.0999   $154.10   $154.10   $154.10  
  Purchase #7 $205.66   12.336%   $231.0302   $231.03   $231.05   $231.00  
  7 purchase totals = $986.96       $1,065.2464   $1,065.24   $1,065.25   $1,065.30