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 $46.96   5.661%   $49.6184   $49.62   $49.60   $49.60  
  Purchase #2 $202.76   10.560%   $224.1715   $224.17   $224.15   $224.20  
  Purchase #3 $133.91   4.149%   $139.4659   $139.47   $139.45   $139.50  
  Purchase #4 $6.44   3.492%   $6.6649   $6.66   $6.65   $6.70  
  Purchase #5 $65.53   4.559%   $68.5175   $68.52   $68.50   $68.50  
  Purchase #6 $212.70   6.171%   $225.8257   $225.83   $225.85   $225.80  
  Purchase #7 $19.26   11.722%   $21.5177   $21.52   $21.50   $21.50  
  7 purchase totals = $687.56       $735.7816   $735.79   $735.70   $735.80