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 $142.47   5.286%   $150.001   $150.00   $150.00   $150.00  
  Purchase #2 $227.81   7.179%   $244.1645   $244.16   $244.15   $244.20  
  Purchase #3 $60.74   11.698%   $67.8454   $67.85   $67.85   $67.80  
  Purchase #4 $97.36   12.360%   $109.3937   $109.39   $109.40   $109.40  
  Purchase #5 $235.71   7.112%   $252.4737   $252.47   $252.45   $252.50  
  Purchase #6 $147.75   9.247%   $161.4124   $161.41   $161.40   $161.40  
  Purchase #7 $215.82   3.315%   $222.9744   $222.97   $222.95   $223.00  
  7 purchase totals = $1,127.66       $1,208.2651   $1,208.25   $1,208.20   $1,208.30