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 $211.57   3.833%   $219.6795   $219.68   $219.70   $219.70  
  Purchase #2 $118.91   9.119%   $129.7534   $129.75   $129.75   $129.80  
  Purchase #3 $54.32   5.378%   $57.2413   $57.24   $57.25   $57.20  
  Purchase #4 $13.84   8.382%   $15.0001   $15.00   $15.00   $15.00  
  Purchase #5 $71.52   8.437%   $77.5541   $77.55   $77.55   $77.60  
  Purchase #6 $248.75   9.591%   $272.6076   $272.61   $272.60   $272.60  
  Purchase #7 $81.66   6.412%   $86.896   $86.90   $86.90   $86.90  
  7 purchase totals = $800.57       $858.7320   $858.73   $858.75   $858.80