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 $79.57   8.577%   $86.3947   $86.39   $86.40   $86.40  
  Purchase #2 $62.79   12.641%   $70.7273   $70.73   $70.75   $70.70  
  Purchase #3 $118.86   10.708%   $131.5875   $131.59   $131.60   $131.60  
  Purchase #4 $11.50   10.154%   $12.6677   $12.67   $12.65   $12.70  
  Purchase #5 $80.75   3.439%   $83.527   $83.53   $83.55   $83.50  
  Purchase #6 $58.40   5.441%   $61.5775   $61.58   $61.60   $61.60  
  Purchase #7 $25.30   5.802%   $26.7679   $26.77   $26.75   $26.80  
  7 purchase totals = $437.17       $473.2496   $473.26   $473.30   $473.30