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 $147.85   6.855%   $157.9851   $157.99   $158.00   $158.00  
  Purchase #2 $16.80   6.606%   $17.9098   $17.91   $17.90   $17.90  
  Purchase #3 $10.52   11.448%   $11.7243   $11.72   $11.70   $11.70  
  Purchase #4 $160.73   9.320%   $175.71   $175.71   $175.70   $175.70  
  Purchase #5 $139.88   4.629%   $146.355   $146.36   $146.35   $146.40  
  Purchase #6 $126.25   5.259%   $132.8895   $132.89   $132.90   $132.90  
  Purchase #7 $176.51   4.811%   $185.0019   $185.00   $185.00   $185.00  
  7 purchase totals = $778.54       $827.5756   $827.58   $827.55   $827.60