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	$174.55	4.853%	$183.0209	$183.02	$183.00	$183.00
Purchase #2	$129.57	8.685%	$140.8232	$140.82	$140.80	$140.80
Purchase #3	$77.60	5.110%	$81.5654	$81.57	$81.55	$81.60
Purchase #4	$62.33	13.872%	$70.9764	$70.98	$71.00	$71.00
Purchase #5	$105.55	8.314%	$114.3254	$114.33	$114.35	$114.30
Purchase #6	$165.38	12.106%	$185.4009	$185.40	$185.40	$185.40
Purchase #7	$220.54	3.117%	$227.4142	$227.41	$227.40	$227.40
7 purchase totals =	$935.52		$1,003.5264	$1,003.53	$1,003.50	$1,003.50