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 $66.33   12.538%   $74.6465   $74.65   $74.65   $74.60  
  Purchase #2 $98.92   13.531%   $112.3049   $112.30   $112.30   $112.30  
  Purchase #3 $207.99   11.395%   $231.6905   $231.69   $231.70   $231.70  
  Purchase #4 $152.89   7.446%   $164.2742   $164.27   $164.25   $164.30  
  Purchase #5 $9.58   8.137%   $10.3595   $10.36   $10.35   $10.40  
  Purchase #6 $150.30   5.469%   $158.5199   $158.52   $158.50   $158.50  
  Purchase #7 $249.72   8.527%   $271.0136   $271.01   $271.00   $271.00  
  7 purchase totals = $935.73       $1,022.8091   $1,022.80   $1,022.75   $1,022.80