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 $207.63   10.615%   $229.6699   $229.67   $229.65   $229.70  
  Purchase #2 $38.96   6.198%   $41.3747   $41.37   $41.35   $41.40  
  Purchase #3 $38.96   8.727%   $42.36   $42.36   $42.35   $42.40  
  Purchase #4 $110.45   6.379%   $117.4956   $117.50   $117.50   $117.50  
  Purchase #5 $53.76   8.122%   $58.1264   $58.13   $58.15   $58.10  
  Purchase #6 $168.94   10.316%   $186.3679   $186.37   $186.35   $186.40  
  Purchase #7 $131.76   7.626%   $141.808   $141.81   $141.80   $141.80  
  7 purchase totals = $750.46       $817.2025   $817.21   $817.15   $817.30