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 $214.79   5.668%   $226.9643   $226.96   $226.95   $227.00  
  Purchase #2 $110.89   5.735%   $117.2495   $117.25   $117.25   $117.20  
  Purchase #3 $154.25   8.169%   $166.8507   $166.85   $166.85   $166.90  
  Purchase #4 $159.65   10.716%   $176.7581   $176.76   $176.75   $176.80  
  Purchase #5 $16.36   7.201%   $17.5381   $17.54   $17.55   $17.50  
  Purchase #6 $113.48   8.651%   $123.2972   $123.30   $123.30   $123.30  
  Purchase #7 $214.88   5.679%   $227.083   $227.08   $227.10   $227.10  
  7 purchase totals = $984.30       $1,055.7409   $1,055.74   $1,055.75   $1,055.80