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 $66.74   12.606%   $75.1532   $75.15   $75.15   $75.20  
  Purchase #2 $248.69   9.754%   $272.9472   $272.95   $272.95   $272.90  
  Purchase #3 $90.41   8.418%   $98.0207   $98.02   $98.00   $98.00  
  Purchase #4 $171.28   3.236%   $176.8226   $176.82   $176.80   $176.80  
  Purchase #5 $53.51   13.326%   $60.6407   $60.64   $60.65   $60.60  
  Purchase #6 $97.87   7.362%   $105.0752   $105.08   $105.10   $105.10  
  Purchase #7 $150.89   6.414%   $160.5681   $160.57   $160.55   $160.60  
  7 purchase totals = $879.39       $949.2277   $949.23   $949.20   $949.20