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 $125.27   4.862%   $131.3606   $131.36   $131.35   $131.40  
  Purchase #2 $113.33   9.127%   $123.6736   $123.67   $123.65   $123.70  
  Purchase #3 $157.58   7.420%   $169.2724   $169.27   $169.25   $169.30  
  Purchase #4 $235.45   11.531%   $262.5997   $262.60   $262.60   $262.60  
  Purchase #5 $166.46   3.380%   $172.0863   $172.09   $172.10   $172.10  
  Purchase #6 $162.44   10.420%   $179.3662   $179.37   $179.35   $179.40  
  Purchase #7 $15.28   10.643%   $16.9063   $16.91   $16.90   $16.90  
  7 purchase totals = $975.81       $1,055.2651   $1,055.27   $1,055.20   $1,055.40