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 $56.97   12.323%   $63.9904   $63.99   $64.00   $64.00  
  Purchase #2 $202.61   6.262%   $215.2974   $215.30   $215.30   $215.30  
  Purchase #3 $237.34   13.497%   $269.3738   $269.37   $269.35   $269.40  
  Purchase #4 $218.68   5.637%   $231.007   $231.01   $231.00   $231.00  
  Purchase #5 $49.78   9.473%   $54.4957   $54.50   $54.50   $54.50  
  Purchase #6 $157.99   11.245%   $175.756   $175.76   $175.75   $175.80  
  Purchase #7 $11.77   10.585%   $13.0159   $13.02   $13.00   $13.00  
  7 purchase totals = $935.14       $1,022.9362   $1,022.95   $1,022.90   $1,023.00