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 $176.80   7.771%   $190.5391   $190.54   $190.55   $190.50  
  Purchase #2 $5.52   8.473%   $5.9877   $5.99   $6.00   $6.00  
  Purchase #3 $18.25   12.835%   $20.5924   $20.59   $20.60   $20.60  
  Purchase #4 $100.85   3.461%   $104.3404   $104.34   $104.35   $104.30  
  Purchase #5 $162.94   8.841%   $177.3455   $177.35   $177.35   $177.30  
  Purchase #6 $207.93   9.420%   $227.517   $227.52   $227.50   $227.50  
  Purchase #7 $34.69   7.353%   $37.2408   $37.24   $37.25   $37.20  
  7 purchase totals = $706.98       $763.5629   $763.57   $763.60   $763.40