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 $60.61   12.110%   $67.9499   $67.95   $67.95   $67.90  
  Purchase #2 $97.28   12.750%   $109.6832   $109.68   $109.70   $109.70  
  Purchase #3 $131.75   10.107%   $145.066   $145.07   $145.05   $145.10  
  Purchase #4 $90.95   10.702%   $100.6835   $100.68   $100.70   $100.70  
  Purchase #5 $45.36   5.589%   $47.8952   $47.90   $47.90   $47.90  
  Purchase #6 $248.74   8.682%   $270.3356   $270.34   $270.35   $270.30  
  Purchase #7 $169.47   11.523%   $188.998   $189.00   $189.00   $189.00  
  7 purchase totals = $844.16       $930.6114   $930.62   $930.65   $930.60