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 $227.90   12.413%   $256.1892   $256.19   $256.20   $256.20  
  Purchase #2 $206.74   3.359%   $213.6844   $213.68   $213.70   $213.70  
  Purchase #3 $163.36   5.567%   $172.4543   $172.45   $172.45   $172.50  
  Purchase #4 $98.61   9.243%   $107.7245   $107.72   $107.70   $107.70  
  Purchase #5 $191.93   12.799%   $216.4951   $216.50   $216.50   $216.50  
  Purchase #6 $242.44   12.642%   $273.0893   $273.09   $273.10   $273.10  
  Purchase #7 $222.68   5.155%   $234.1592   $234.16   $234.15   $234.20  
  7 purchase totals = $1,353.66       $1,473.7960   $1,473.79   $1,473.80   $1,473.90