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 $64.38   13.752%   $73.2335   $73.23   $73.25   $73.20  
  Purchase #2 $103.29   4.818%   $108.2665   $108.27   $108.25   $108.30  
  Purchase #3 $154.64   9.715%   $169.6633   $169.66   $169.65   $169.70  
  Purchase #4 $5.42   6.448%   $5.7695   $5.77   $5.75   $5.80  
  Purchase #5 $241.99   6.800%   $258.4453   $258.45   $258.45   $258.40  
  Purchase #6 $171.58   8.250%   $185.7354   $185.74   $185.75   $185.70  
  Purchase #7 $120.65   3.152%   $124.4529   $124.45   $124.45   $124.50  
  7 purchase totals = $861.95       $925.5664   $925.57   $925.55   $925.60