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 $211.79   9.461%   $231.8275   $231.83   $231.85   $231.80  
  Purchase #2 $225.92   13.249%   $255.8521   $255.85   $255.85   $255.90  
  Purchase #3 $216.76   7.354%   $232.7005   $232.70   $232.70   $232.70  
  Purchase #4 $213.62   5.704%   $225.8049   $225.80   $225.80   $225.80  
  Purchase #5 $212.45   10.645%   $235.0653   $235.07   $235.05   $235.10  
  Purchase #6 $116.95   4.619%   $122.3519   $122.35   $122.35   $122.40  
  Purchase #7 $244.28   12.435%   $274.6562   $274.66   $274.65   $274.70  
  7 purchase totals = $1,441.77       $1,578.2584   $1,578.26   $1,578.25   $1,578.40