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 $208.53   7.466%   $224.0988   $224.10   $224.10   $224.10  
  Purchase #2 $77.67   9.754%   $85.2459   $85.25   $85.25   $85.20  
  Purchase #3 $121.52   9.555%   $133.1312   $133.13   $133.15   $133.10  
  Purchase #4 $218.43   13.700%   $248.3549   $248.35   $248.35   $248.40  
  Purchase #5 $217.96   5.137%   $229.1566   $229.16   $229.15   $229.20  
  Purchase #6 $51.69   13.241%   $58.5343   $58.53   $58.55   $58.50  
  Purchase #7 $24.53   8.316%   $26.5699   $26.57   $26.55   $26.60  
  7 purchase totals = $920.33       $1,005.0916   $1,005.09   $1,005.10   $1,005.10