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 $66.59   11.552%   $74.2825   $74.28   $74.30   $74.30  
  Purchase #2 $156.39   12.761%   $176.3469   $176.35   $176.35   $176.30  
  Purchase #3 $196.61   3.170%   $202.8425   $202.84   $202.85   $202.80  
  Purchase #4 $161.77   8.280%   $175.1646   $175.16   $175.15   $175.20  
  Purchase #5 $86.75   3.280%   $89.5954   $89.60   $89.60   $89.60  
  Purchase #6 $157.36   12.282%   $176.687   $176.69   $176.70   $176.70  
  Purchase #7 $176.25   12.468%   $198.2249   $198.22   $198.20   $198.20  
  7 purchase totals = $1,001.72       $1,093.1438   $1,093.14   $1,093.15   $1,093.10