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 $165.76   11.161%   $184.2605   $184.26   $184.25   $184.30  
  Purchase #2 $246.32   9.571%   $269.8953   $269.90   $269.90   $269.90  
  Purchase #3 $117.91   12.496%   $132.644   $132.64   $132.65   $132.60  
  Purchase #4 $89.97   12.780%   $101.4682   $101.47   $101.45   $101.50  
  Purchase #5 $214.88   10.569%   $237.5907   $237.59   $237.60   $237.60  
  Purchase #6 $58.33   11.788%   $65.2059   $65.21   $65.20   $65.20  
  Purchase #7 $247.80   8.426%   $268.6796   $268.68   $268.70   $268.70  
  7 purchase totals = $1,140.97       $1,259.7442   $1,259.75   $1,259.75   $1,259.80