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 $63.48   5.381%   $66.8959   $66.90   $66.90   $66.90  
  Purchase #2 $242.64   4.137%   $252.678   $252.68   $252.70   $252.70  
  Purchase #3 $105.67   5.534%   $111.5178   $111.52   $111.50   $111.50  
  Purchase #4 $69.88   9.844%   $76.759   $76.76   $76.75   $76.80  
  Purchase #5 $47.27   10.735%   $52.3444   $52.34   $52.35   $52.30  
  Purchase #6 $232.52   11.591%   $259.4714   $259.47   $259.45   $259.50  
  Purchase #7 $237.66   5.615%   $251.0046   $251.00   $251.00   $251.00  
  7 purchase totals = $999.12       $1,070.6711   $1,070.67   $1,070.65   $1,070.70