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 $67.93   9.818%   $74.5994   $74.60   $74.60   $74.60  
  Purchase #2 $249.99   7.173%   $267.9218   $267.92   $267.90   $267.90  
  Purchase #3 $109.63   4.225%   $114.2619   $114.26   $114.25   $114.30  
  Purchase #4 $52.89   8.255%   $57.2561   $57.26   $57.25   $57.30  
  Purchase #5 $41.38   7.424%   $44.4521   $44.45   $44.45   $44.50  
  Purchase #6 $120.69   12.362%   $135.6097   $135.61   $135.60   $135.60  
  Purchase #7 $140.50   7.835%   $151.5082   $151.51   $151.50   $151.50  
  7 purchase totals = $783.01       $845.6092   $845.61   $845.55   $845.70