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 $185.68   3.698%   $192.5464   $192.55   $192.55   $192.50  
  Purchase #2 $67.74   12.246%   $76.0354   $76.04   $76.05   $76.00  
  Purchase #3 $51.99   13.492%   $59.0045   $59.00   $59.00   $59.00  
  Purchase #4 $115.39   11.331%   $128.4648   $128.46   $128.45   $128.50  
  Purchase #5 $60.52   10.434%   $66.8347   $66.83   $66.85   $66.80  
  Purchase #6 $215.69   5.860%   $228.3294   $228.33   $228.35   $228.30  
  Purchase #7 $22.88   11.519%   $25.5155   $25.52   $25.50   $25.50  
  7 purchase totals = $719.89       $776.7307   $776.73   $776.75   $776.60