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 $169.93   8.728%   $184.7615   $184.76   $184.75   $184.80  
  Purchase #2 $189.50   10.704%   $209.7841   $209.78   $209.80   $209.80  
  Purchase #3 $247.30   4.818%   $259.2149   $259.21   $259.20   $259.20  
  Purchase #4 $66.87   7.246%   $71.7154   $71.72   $71.70   $71.70  
  Purchase #5 $152.90   7.523%   $164.4027   $164.40   $164.40   $164.40  
  Purchase #6 $120.85   4.584%   $126.3898   $126.39   $126.40   $126.40  
  Purchase #7 $41.26   11.859%   $46.153   $46.15   $46.15   $46.20  
  7 purchase totals = $988.61       $1,062.4214   $1,062.41   $1,062.40   $1,062.50