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 $62.56   13.415%   $70.9524   $70.95   $70.95   $71.00  
  Purchase #2 $247.97   5.365%   $261.2736   $261.27   $261.25   $261.30  
  Purchase #3 $42.97   11.268%   $47.8119   $47.81   $47.80   $47.80  
  Purchase #4 $30.77   4.820%   $32.2531   $32.25   $32.25   $32.30  
  Purchase #5 $192.58   6.731%   $205.5426   $205.54   $205.55   $205.50  
  Purchase #6 $217.42   5.146%   $228.6084   $228.61   $228.60   $228.60  
  Purchase #7 $99.53   5.499%   $105.0032   $105.00   $105.00   $105.00  
  7 purchase totals = $893.80       $951.4452   $951.43   $951.40   $951.50