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 $34.99   3.688%   $36.2804   $36.28   $36.30   $36.30  
  Purchase #2 $235.80   9.144%   $257.3616   $257.36   $257.35   $257.40  
  Purchase #3 $210.57   7.513%   $226.3901   $226.39   $226.40   $226.40  
  Purchase #4 $145.58   12.685%   $164.0468   $164.05   $164.05   $164.00  
  Purchase #5 $239.93   8.609%   $260.5856   $260.59   $260.60   $260.60  
  Purchase #6 $194.61   3.490%   $201.4019   $201.40   $201.40   $201.40  
  Purchase #7 $136.63   10.208%   $150.5772   $150.58   $150.60   $150.60  
  7 purchase totals = $1,198.11       $1,296.6436   $1,296.65   $1,296.70   $1,296.70