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	$99.88	12.780%	$112.6447	$112.64	$112.65	$112.60
Purchase #2	$153.40	9.816%	$168.4577	$168.46	$168.45	$168.50
Purchase #3	$128.37	9.369%	$140.397	$140.40	$140.40	$140.40
Purchase #4	$227.51	10.215%	$250.7501	$250.75	$250.75	$250.80
Purchase #5	$133.90	4.735%	$140.2402	$140.24	$140.25	$140.20
Purchase #6	$238.72	10.553%	$263.9121	$263.91	$263.90	$263.90
Purchase #7	$38.98	11.309%	$43.3882	$43.39	$43.40	$43.40
7 purchase totals =	$1,020.76		$1,119.7900	$1,119.79	$1,119.80	$1,119.80