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 $156.94   11.277%   $174.6381   $174.64   $174.65   $174.60  
  Purchase #2 $92.66   4.102%   $96.4609   $96.46   $96.45   $96.50  
  Purchase #3 $241.47   7.217%   $258.8969   $258.90   $258.90   $258.90  
  Purchase #4 $249.67   9.821%   $274.1901   $274.19   $274.20   $274.20  
  Purchase #5 $110.50   4.636%   $115.6228   $115.62   $115.60   $115.60  
  Purchase #6 $221.53   13.832%   $252.172   $252.17   $252.15   $252.20  
  Purchase #7 $154.27   13.710%   $175.4204   $175.42   $175.40   $175.40  
  7 purchase totals = $1,227.04       $1,347.4012   $1,347.40   $1,347.35   $1,347.40