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 $96.56   4.230%   $100.6445   $100.64   $100.65   $100.60  
  Purchase #2 $57.73   7.392%   $61.9974   $62.00   $62.00   $62.00  
  Purchase #3 $156.32   11.852%   $174.847   $174.85   $174.85   $174.80  
  Purchase #4 $162.28   4.409%   $169.4349   $169.43   $169.45   $169.40  
  Purchase #5 $73.33   8.119%   $79.2837   $79.28   $79.30   $79.30  
  Purchase #6 $244.34   3.233%   $252.2395   $252.24   $252.25   $252.20  
  Purchase #7 $103.33   10.847%   $114.5382   $114.54   $114.55   $114.50  
  7 purchase totals = $893.89       $952.9852   $952.98   $953.05   $952.80