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 $32.96   5.788%   $34.8677   $34.87   $34.85   $34.90  
  Purchase #2 $211.91   3.483%   $219.2908   $219.29   $219.30   $219.30  
  Purchase #3 $154.63   9.146%   $168.7725   $168.77   $168.75   $168.80  
  Purchase #4 $113.27   8.274%   $122.642   $122.64   $122.65   $122.60  
  Purchase #5 $184.59   7.527%   $198.4841   $198.48   $198.50   $198.50  
  Purchase #6 $38.61   3.826%   $40.0872   $40.09   $40.10   $40.10  
  Purchase #7 $219.75   4.317%   $229.2366   $229.24   $229.25   $229.20  
  7 purchase totals = $955.72       $1,013.3809   $1,013.38   $1,013.40   $1,013.40