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 $202.36   12.214%   $227.0763   $227.08   $227.10   $227.10  
  Purchase #2 $125.69   11.351%   $139.9571   $139.96   $139.95   $140.00  
  Purchase #3 $134.92   12.550%   $151.8525   $151.85   $151.85   $151.90  
  Purchase #4 $163.39   5.474%   $172.334   $172.33   $172.35   $172.30  
  Purchase #5 $115.50   8.180%   $124.9479   $124.95   $124.95   $124.90  
  Purchase #6 $194.61   5.667%   $205.6385   $205.64   $205.65   $205.60  
  Purchase #7 $68.35   10.704%   $75.6662   $75.67   $75.65   $75.70  
  7 purchase totals = $1,004.82       $1,097.4725   $1,097.48   $1,097.50   $1,097.50