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 $96.93   13.581%   $110.0941   $110.09   $110.10   $110.10  
  Purchase #2 $82.80   13.174%   $93.7081   $93.71   $93.70   $93.70  
  Purchase #3 $89.89   8.606%   $97.6259   $97.63   $97.65   $97.60  
  Purchase #4 $26.88   13.200%   $30.4282   $30.43   $30.45   $30.40  
  Purchase #5 $49.82   13.810%   $56.7001   $56.70   $56.70   $56.70  
  Purchase #6 $120.38   11.300%   $133.9829   $133.98   $134.00   $134.00  
  Purchase #7 $221.74   5.646%   $234.2594   $234.26   $234.25   $234.30  
  7 purchase totals = $688.44       $756.7987   $756.80   $756.85   $756.80