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 $95.56   3.119%   $98.5405   $98.54   $98.55   $98.50  
  Purchase #2 $223.40   13.337%   $253.1949   $253.19   $253.20   $253.20  
  Purchase #3 $182.26   7.136%   $195.2661   $195.27   $195.25   $195.30  
  Purchase #4 $170.86   13.772%   $194.3908   $194.39   $194.40   $194.40  
  Purchase #5 $170.95   12.412%   $192.1683   $192.17   $192.15   $192.20  
  Purchase #6 $108.49   11.224%   $120.6669   $120.67   $120.65   $120.70  
  Purchase #7 $159.64   13.525%   $181.2313   $181.23   $181.25   $181.20  
  7 purchase totals = $1,111.16       $1,235.4588   $1,235.46   $1,235.45   $1,235.50