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 $204.49   10.147%   $225.2396   $225.24   $225.25   $225.20  
  Purchase #2 $218.53   7.177%   $234.2139   $234.21   $234.20   $234.20  
  Purchase #3 $247.29   6.225%   $262.6838   $262.68   $262.70   $262.70  
  Purchase #4 $127.99   10.594%   $141.5493   $141.55   $141.55   $141.50  
  Purchase #5 $117.27   6.466%   $124.8527   $124.85   $124.85   $124.90  
  Purchase #6 $160.66   12.396%   $180.5754   $180.58   $180.60   $180.60  
  Purchase #7 $35.96   6.510%   $38.301   $38.30   $38.30   $38.30  
  7 purchase totals = $1,112.19       $1,207.4157   $1,207.41   $1,207.45   $1,207.40