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 $183.73   13.276%   $208.122   $208.12   $208.10   $208.10  
  Purchase #2 $93.56   7.847%   $100.9017   $100.90   $100.90   $100.90  
  Purchase #3 $32.81   7.365%   $35.2265   $35.23   $35.25   $35.20  
  Purchase #4 $53.90   13.190%   $61.0094   $61.01   $61.00   $61.00  
  Purchase #5 $247.87   4.766%   $259.6835   $259.68   $259.70   $259.70  
  Purchase #6 $66.44   6.140%   $70.5194   $70.52   $70.50   $70.50  
  Purchase #7 $61.62   13.354%   $69.8487   $69.85   $69.85   $69.80  
  7 purchase totals = $739.93       $805.3112   $805.31   $805.30   $805.20