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 $134.81   13.693%   $153.2695   $153.27   $153.25   $153.30  
  Purchase #2 $151.37   12.466%   $170.2398   $170.24   $170.25   $170.20  
  Purchase #3 $123.94   6.822%   $132.3952   $132.40   $132.40   $132.40  
  Purchase #4 $233.34   4.581%   $244.0293   $244.03   $244.05   $244.00  
  Purchase #5 $159.65   3.671%   $165.5108   $165.51   $165.50   $165.50  
  Purchase #6 $63.65   6.416%   $67.7338   $67.73   $67.75   $67.70  
  Purchase #7 $208.82   5.206%   $219.6912   $219.69   $219.70   $219.70  
  7 purchase totals = $1,075.58       $1,152.8696   $1,152.87   $1,152.90   $1,152.80