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 $49.54   8.140%   $53.5726   $53.57   $53.55   $53.60  
  Purchase #2 $166.72   9.319%   $182.2566   $182.26   $182.25   $182.30  
  Purchase #3 $111.74   6.457%   $118.9551   $118.96   $118.95   $119.00  
  Purchase #4 $192.41   8.273%   $208.3281   $208.33   $208.35   $208.30  
  Purchase #5 $176.59   7.724%   $190.2298   $190.23   $190.25   $190.20  
  Purchase #6 $82.52   12.703%   $93.0025   $93.00   $93.00   $93.00  
  Purchase #7 $82.64   11.186%   $91.8841   $91.88   $91.90   $91.90  
  7 purchase totals = $862.16       $938.2288   $938.23   $938.25   $938.30