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 $24.85   6.818%   $26.5443   $26.54   $26.55   $26.50  
  Purchase #2 $53.71   13.665%   $61.0495   $61.05   $61.05   $61.00  
  Purchase #3 $177.65   3.472%   $183.818   $183.82   $183.80   $183.80  
  Purchase #4 $77.65   8.162%   $83.9878   $83.99   $84.00   $84.00  
  Purchase #5 $160.37   11.569%   $178.9232   $178.92   $178.90   $178.90  
  Purchase #6 $145.76   5.175%   $153.3031   $153.30   $153.30   $153.30  
  Purchase #7 $224.58   3.572%   $232.602   $232.60   $232.60   $232.60  
  7 purchase totals = $864.57       $920.2279   $920.22   $920.20   $920.10