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 $166.42   12.755%   $187.6469   $187.65   $187.65   $187.60  
  Purchase #2 $237.30   12.232%   $266.3265   $266.33   $266.35   $266.30  
  Purchase #3 $84.40   13.740%   $95.9966   $96.00   $96.00   $96.00  
  Purchase #4 $204.25   8.683%   $221.985   $221.99   $222.00   $222.00  
  Purchase #5 $104.47   7.610%   $112.4202   $112.42   $112.40   $112.40  
  Purchase #6 $156.31   3.398%   $161.6214   $161.62   $161.60   $161.60  
  Purchase #7 $248.32   8.557%   $269.5687   $269.57   $269.55   $269.60  
  7 purchase totals = $1,201.47       $1,315.5653   $1,315.58   $1,315.55   $1,315.50