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 $185.49   13.651%   $210.8112   $210.81   $210.80   $210.80  
  Purchase #2 $28.69   9.256%   $31.3455   $31.35   $31.35   $31.30  
  Purchase #3 $62.72   4.394%   $65.4759   $65.48   $65.50   $65.50  
  Purchase #4 $161.31   7.834%   $173.947   $173.95   $173.95   $173.90  
  Purchase #5 $97.37   8.239%   $105.3923   $105.39   $105.40   $105.40  
  Purchase #6 $137.67   5.527%   $145.279   $145.28   $145.30   $145.30  
  Purchase #7 $183.39   5.431%   $193.3499   $193.35   $193.35   $193.30  
  7 purchase totals = $856.64       $925.6008   $925.61   $925.65   $925.50