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 $141.79   8.231%   $153.4607   $153.46   $153.45   $153.50  
  Purchase #2 $88.25   8.340%   $95.6101   $95.61   $95.60   $95.60  
  Purchase #3 $97.46   4.844%   $102.181   $102.18   $102.20   $102.20  
  Purchase #4 $233.95   13.376%   $265.2432   $265.24   $265.25   $265.20  
  Purchase #5 $187.97   13.220%   $212.8196   $212.82   $212.80   $212.80  
  Purchase #6 $53.81   13.162%   $60.8925   $60.89   $60.90   $60.90  
  Purchase #7 $64.63   9.623%   $70.8493   $70.85   $70.85   $70.80  
  7 purchase totals = $867.86       $961.0564   $961.05   $961.05   $961.00