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 $47.50   5.323%   $50.0284   $50.03   $50.05   $50.00  
  Purchase #2 $119.50   3.241%   $123.373   $123.37   $123.35   $123.40  
  Purchase #3 $89.27   7.530%   $95.992   $95.99   $96.00   $96.00  
  Purchase #4 $169.26   5.254%   $178.1529   $178.15   $178.15   $178.20  
  Purchase #5 $192.66   5.232%   $202.74   $202.74   $202.75   $202.70  
  Purchase #6 $92.44   5.335%   $97.3717   $97.37   $97.35   $97.40  
  Purchase #7 $231.72   10.595%   $256.2707   $256.27   $256.25   $256.30  
  7 purchase totals = $942.35       $1,003.9287   $1,003.92   $1,003.90   $1,004.00