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 $62.62   5.838%   $66.2758   $66.28   $66.30   $66.30  
  Purchase #2 $113.99   4.656%   $119.2974   $119.30   $119.30   $119.30  
  Purchase #3 $108.88   7.311%   $116.8402   $116.84   $116.85   $116.80  
  Purchase #4 $142.72   6.794%   $152.4164   $152.42   $152.40   $152.40  
  Purchase #5 $119.51   11.836%   $133.6552   $133.66   $133.65   $133.70  
  Purchase #6 $133.52   13.441%   $151.4664   $151.47   $151.45   $151.50  
  Purchase #7 $147.80   6.415%   $157.2814   $157.28   $157.30   $157.30  
  7 purchase totals = $829.04       $897.2328   $897.25   $897.25   $897.30