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 $62.96   12.678%   $70.9421   $70.94   $70.95   $70.90  
  Purchase #2 $226.38   8.538%   $245.7083   $245.71   $245.70   $245.70  
  Purchase #3 $110.32   10.786%   $122.2191   $122.22   $122.20   $122.20  
  Purchase #4 $238.73   7.726%   $257.1743   $257.17   $257.15   $257.20  
  Purchase #5 $218.52   13.698%   $248.4529   $248.45   $248.45   $248.50  
  Purchase #6 $125.26   5.843%   $132.5789   $132.58   $132.60   $132.60  
  Purchase #7 $20.36   10.857%   $22.5705   $22.57   $22.55   $22.60  
  7 purchase totals = $1,002.53       $1,099.6461   $1,099.64   $1,099.60   $1,099.70