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 $113.29   11.531%   $126.3535   $126.35   $126.35   $126.40  
  Purchase #2 $186.92   11.272%   $207.9896   $207.99   $208.00   $208.00  
  Purchase #3 $246.59   10.109%   $271.5178   $271.52   $271.50   $271.50  
  Purchase #4 $65.32   12.688%   $73.6078   $73.61   $73.60   $73.60  
  Purchase #5 $7.98   7.174%   $8.5525   $8.55   $8.55   $8.60  
  Purchase #6 $218.92   12.381%   $246.0245   $246.02   $246.00   $246.00  
  Purchase #7 $67.83   12.436%   $76.2653   $76.27   $76.25   $76.30  
  7 purchase totals = $906.85       $1,010.3110   $1,010.31   $1,010.25   $1,010.40