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 $190.39   9.632%   $208.7284   $208.73   $208.75   $208.70  
  Purchase #2 $149.55   4.846%   $156.7972   $156.80   $156.80   $156.80  
  Purchase #3 $29.89   4.786%   $31.3205   $31.32   $31.30   $31.30  
  Purchase #4 $176.87   3.281%   $182.6731   $182.67   $182.65   $182.70  
  Purchase #5 $126.69   11.708%   $141.5229   $141.52   $141.50   $141.50  
  Purchase #6 $250.29   7.240%   $268.411   $268.41   $268.40   $268.40  
  Purchase #7 $65.83   5.369%   $69.3644   $69.36   $69.35   $69.40  
  7 purchase totals = $989.51       $1,058.8175   $1,058.81   $1,058.75   $1,058.80