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 $90.32   3.714%   $93.6745   $93.67   $93.65   $93.70  
  Purchase #2 $55.64   11.491%   $62.0336   $62.03   $62.05   $62.00  
  Purchase #3 $59.36   10.535%   $65.6136   $65.61   $65.60   $65.60  
  Purchase #4 $28.96   4.259%   $30.1934   $30.19   $30.20   $30.20  
  Purchase #5 $232.40   10.855%   $257.627   $257.63   $257.65   $257.60  
  Purchase #6 $5.31   12.143%   $5.9548   $5.95   $5.95   $6.00  
  Purchase #7 $44.91   5.812%   $47.5202   $47.52   $47.50   $47.50  
  7 purchase totals = $516.90       $562.6171   $562.60   $562.60   $562.60