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 $152.54   3.304%   $157.5799   $157.58   $157.60   $157.60  
  Purchase #2 $89.91   5.163%   $94.5521   $94.55   $94.55   $94.60  
  Purchase #3 $234.38   13.611%   $266.2815   $266.28   $266.30   $266.30  
  Purchase #4 $137.35   10.502%   $151.7745   $151.77   $151.75   $151.80  
  Purchase #5 $182.75   7.562%   $196.5696   $196.57   $196.55   $196.60  
  Purchase #6 $149.77   6.261%   $159.1471   $159.15   $159.15   $159.10  
  Purchase #7 $218.81   3.636%   $226.7659   $226.77   $226.75   $226.80  
  7 purchase totals = $1,165.51       $1,252.6706   $1,252.67   $1,252.65   $1,252.80