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 $183.57   10.313%   $202.5016   $202.50   $202.50   $202.50  
  Purchase #2 $156.35   13.147%   $176.9053   $176.91   $176.90   $176.90  
  Purchase #3 $144.85   8.611%   $157.323   $157.32   $157.30   $157.30  
  Purchase #4 $131.76   4.757%   $138.0278   $138.03   $138.05   $138.00  
  Purchase #5 $194.65   11.349%   $216.7408   $216.74   $216.75   $216.70  
  Purchase #6 $17.92   5.491%   $18.904   $18.90   $18.90   $18.90  
  Purchase #7 $150.47   9.843%   $165.2808   $165.28   $165.30   $165.30  
  7 purchase totals = $979.57       $1,075.6833   $1,075.68   $1,075.70   $1,075.60