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 $57.48   7.246%   $61.645   $61.65   $61.65   $61.60  
  Purchase #2 $158.64   11.424%   $176.763   $176.76   $176.75   $176.80  
  Purchase #3 $193.62   5.322%   $203.9245   $203.92   $203.90   $203.90  
  Purchase #4 $69.42   5.754%   $73.4144   $73.41   $73.40   $73.40  
  Purchase #5 $95.59   6.409%   $101.7164   $101.72   $101.70   $101.70  
  Purchase #6 $230.61   12.241%   $258.839   $258.84   $258.85   $258.80  
  Purchase #7 $26.31   3.275%   $27.1717   $27.17   $27.15   $27.20  
  7 purchase totals = $831.67       $903.4740   $903.47   $903.40   $903.40