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 $202.76   12.255%   $227.6082   $227.61   $227.60   $227.60  
  Purchase #2 $43.49   10.738%   $48.16   $48.16   $48.15   $48.20  
  Purchase #3 $83.81   7.152%   $89.8041   $89.80   $89.80   $89.80  
  Purchase #4 $229.54   4.145%   $239.0544   $239.05   $239.05   $239.10  
  Purchase #5 $108.57   4.545%   $113.5045   $113.50   $113.50   $113.50  
  Purchase #6 $155.81   6.307%   $165.6369   $165.64   $165.65   $165.60  
  Purchase #7 $130.35   7.434%   $140.0402   $140.04   $140.05   $140.00  
  7 purchase totals = $954.33       $1,023.8083   $1,023.80   $1,023.80   $1,023.80