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 $88.93   8.207%   $96.2285   $96.23   $96.25   $96.20  
  Purchase #2 $170.98   13.329%   $193.7699   $193.77   $193.75   $193.80  
  Purchase #3 $14.81   4.518%   $15.4791   $15.48   $15.50   $15.50  
  Purchase #4 $234.57   8.681%   $254.933   $254.93   $254.95   $254.90  
  Purchase #5 $223.92   10.852%   $248.2198   $248.22   $248.20   $248.20  
  Purchase #6 $93.53   6.413%   $99.5281   $99.53   $99.55   $99.50  
  Purchase #7 $113.64   8.399%   $123.1846   $123.18   $123.20   $123.20  
  7 purchase totals = $940.38       $1,031.3430   $1,031.34   $1,031.40   $1,031.30