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 $205.63   10.792%   $227.8216   $227.82   $227.80   $227.80  
  Purchase #2 $52.45   5.664%   $55.4208   $55.42   $55.40   $55.40  
  Purchase #3 $202.43   6.871%   $216.339   $216.34   $216.35   $216.30  
  Purchase #4 $117.67   4.833%   $123.357   $123.36   $123.35   $123.40  
  Purchase #5 $141.88   13.805%   $161.4665   $161.47   $161.45   $161.50  
  Purchase #6 $106.57   10.439%   $117.6948   $117.69   $117.70   $117.70  
  Purchase #7 $134.81   5.768%   $142.5858   $142.59   $142.60   $142.60  
  7 purchase totals = $961.44       $1,044.6855   $1,044.69   $1,044.65   $1,044.70