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 $219.77   12.349%   $246.9094   $246.91   $246.90   $246.90  
  Purchase #2 $61.83   8.442%   $67.0497   $67.05   $67.05   $67.00  
  Purchase #3 $67.70   12.804%   $76.3683   $76.37   $76.35   $76.40  
  Purchase #4 $67.66   4.871%   $70.9557   $70.96   $70.95   $71.00  
  Purchase #5 $208.61   9.405%   $228.2298   $228.23   $228.25   $228.20  
  Purchase #6 $208.67   5.389%   $219.9152   $219.92   $219.90   $219.90  
  Purchase #7 $88.87   11.402%   $99.003   $99.00   $99.00   $99.00  
  7 purchase totals = $923.11       $1,008.4311   $1,008.44   $1,008.40   $1,008.40