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 $111.63   5.291%   $117.5363   $117.54   $117.55   $117.50  
  Purchase #2 $246.93   12.337%   $277.3938   $277.39   $277.40   $277.40  
  Purchase #3 $45.92   3.629%   $47.5864   $47.59   $47.60   $47.60  
  Purchase #4 $158.64   11.147%   $176.3236   $176.32   $176.30   $176.30  
  Purchase #5 $239.77   11.214%   $266.6578   $266.66   $266.65   $266.70  
  Purchase #6 $12.61   13.417%   $14.3019   $14.30   $14.30   $14.30  
  Purchase #7 $169.58   13.229%   $192.0137   $192.01   $192.00   $192.00  
  7 purchase totals = $985.08       $1,091.8135   $1,091.81   $1,091.80   $1,091.80