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 $56.80   10.779%   $62.9225   $62.92   $62.90   $62.90  
  Purchase #2 $224.34   4.706%   $234.8974   $234.90   $234.90   $234.90  
  Purchase #3 $73.34   3.137%   $75.6407   $75.64   $75.65   $75.60  
  Purchase #4 $211.77   10.488%   $233.9804   $233.98   $234.00   $234.00  
  Purchase #5 $235.86   9.350%   $257.9129   $257.91   $257.90   $257.90  
  Purchase #6 $90.50   7.186%   $97.0033   $97.00   $97.00   $97.00  
  Purchase #7 $21.45   11.637%   $23.9461   $23.95   $23.95   $23.90  
  7 purchase totals = $914.06       $986.3033   $986.30   $986.30   $986.20