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 $176.62   10.122%   $194.4975   $194.50   $194.50   $194.50  
  Purchase #2 $163.55   12.598%   $184.154   $184.15   $184.15   $184.20  
  Purchase #3 $245.48   13.340%   $278.227   $278.23   $278.25   $278.20  
  Purchase #4 $123.87   5.556%   $130.7522   $130.75   $130.75   $130.80  
  Purchase #5 $167.69   9.867%   $184.236   $184.24   $184.25   $184.20  
  Purchase #6 $120.69   5.745%   $127.6236   $127.62   $127.60   $127.60  
  Purchase #7 $142.73   9.182%   $155.8355   $155.84   $155.85   $155.80  
  7 purchase totals = $1,140.63       $1,255.3258   $1,255.33   $1,255.35   $1,255.30