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 $246.55   11.238%   $274.2573   $274.26   $274.25   $274.30  
  Purchase #2 $14.71   4.724%   $15.4049   $15.40   $15.40   $15.40  
  Purchase #3 $222.62   8.545%   $241.6429   $241.64   $241.65   $241.60  
  Purchase #4 $120.54   12.222%   $135.2724   $135.27   $135.25   $135.30  
  Purchase #5 $78.60   11.480%   $87.6233   $87.62   $87.60   $87.60  
  Purchase #6 $210.52   6.364%   $223.9175   $223.92   $223.90   $223.90  
  Purchase #7 $241.78   9.805%   $265.4865   $265.49   $265.50   $265.50  
  7 purchase totals = $1,135.32       $1,243.6048   $1,243.60   $1,243.55   $1,243.60