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 $168.67   13.284%   $191.0761   $191.08   $191.10   $191.10  
  Purchase #2 $85.74   8.406%   $92.9473   $92.95   $92.95   $92.90  
  Purchase #3 $235.28   13.567%   $267.2004   $267.20   $267.20   $267.20  
  Purchase #4 $147.63   6.856%   $157.7515   $157.75   $157.75   $157.80  
  Purchase #5 $203.44   8.608%   $220.9521   $220.95   $220.95   $221.00  
  Purchase #6 $92.50   5.847%   $97.9085   $97.91   $97.90   $97.90  
  Purchase #7 $63.95   5.697%   $67.5932   $67.59   $67.60   $67.60  
  7 purchase totals = $997.21       $1,095.4291   $1,095.43   $1,095.45   $1,095.50