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 $214.46   8.112%   $231.857   $231.86   $231.85   $231.90  
  Purchase #2 $23.96   10.863%   $26.5628   $26.56   $26.55   $26.60  
  Purchase #3 $44.87   9.408%   $49.0914   $49.09   $49.10   $49.10  
  Purchase #4 $246.69   8.851%   $268.5245   $268.52   $268.50   $268.50  
  Purchase #5 $183.36   9.151%   $200.1393   $200.14   $200.15   $200.10  
  Purchase #6 $72.62   12.310%   $81.5595   $81.56   $81.55   $81.60  
  Purchase #7 $100.51   3.674%   $104.2027   $104.20   $104.20   $104.20  
  7 purchase totals = $886.47       $961.9372   $961.93   $961.90   $962.00