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 $58.25   7.435%   $62.5809   $62.58   $62.60   $62.60  
  Purchase #2 $74.85   6.301%   $79.5663   $79.57   $79.55   $79.60  
  Purchase #3 $207.96   12.857%   $234.6974   $234.70   $234.70   $234.70  
  Purchase #4 $233.37   4.422%   $243.6896   $243.69   $243.70   $243.70  
  Purchase #5 $127.61   13.558%   $144.9114   $144.91   $144.90   $144.90  
  Purchase #6 $125.65   6.218%   $133.4629   $133.46   $133.45   $133.50  
  Purchase #7 $21.36   6.870%   $22.8274   $22.83   $22.85   $22.80  
  7 purchase totals = $849.05       $921.7359   $921.74   $921.75   $921.80