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 $63.97   5.107%   $67.2369   $67.24   $67.25   $67.20  
  Purchase #2 $231.57   5.208%   $243.6302   $243.63   $243.65   $243.60  
  Purchase #3 $175.83   8.828%   $191.3523   $191.35   $191.35   $191.40  
  Purchase #4 $182.94   6.758%   $195.3031   $195.30   $195.30   $195.30  
  Purchase #5 $77.68   13.293%   $88.006   $88.01   $88.00   $88.00  
  Purchase #6 $239.33   10.145%   $263.61   $263.61   $263.60   $263.60  
  Purchase #7 $230.89   13.720%   $262.5681   $262.57   $262.55   $262.60  
  7 purchase totals = $1,202.21       $1,311.7066   $1,311.71   $1,311.70   $1,311.70