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	$244.47	5.539%	$258.0112	$258.01	$258.00	$258.00
Purchase #2	$193.96	6.612%	$206.7846	$206.78	$206.80	$206.80
Purchase #3	$40.91	5.636%	$43.2157	$43.22	$43.20	$43.20
Purchase #4	$225.85	8.803%	$245.7316	$245.73	$245.75	$245.70
Purchase #5	$53.97	10.139%	$59.442	$59.44	$59.45	$59.40
Purchase #6	$47.30	12.748%	$53.3298	$53.33	$53.35	$53.30
Purchase #7	$59.65	11.209%	$66.3362	$66.34	$66.35	$66.30
7 purchase totals =	$866.11		$932.8511	$932.85	$932.90	$932.70