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 $98.94   4.613%   $103.5041   $103.50   $103.50   $103.50  
  Purchase #2 $191.56   8.564%   $207.9652   $207.97   $207.95   $208.00  
  Purchase #3 $96.90   9.488%   $106.0939   $106.09   $106.10   $106.10  
  Purchase #4 $123.76   4.602%   $129.4554   $129.46   $129.45   $129.50  
  Purchase #5 $247.36   13.857%   $281.6367   $281.64   $281.65   $281.60  
  Purchase #6 $238.57   9.167%   $260.4397   $260.44   $260.45   $260.40  
  Purchase #7 $72.26   9.772%   $79.3212   $79.32   $79.30   $79.30  
  7 purchase totals = $1,069.35       $1,168.4162   $1,168.42   $1,168.40   $1,168.40