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	$73.72	4.118%	$76.7558	$76.76	$76.75	$76.80
Purchase #2	$97.41	13.864%	$110.9149	$110.91	$110.90	$110.90
Purchase #3	$148.40	4.682%	$155.3481	$155.35	$155.35	$155.30
Purchase #4	$98.58	4.758%	$103.2704	$103.27	$103.25	$103.30
Purchase #5	$105.35	9.572%	$115.4341	$115.43	$115.45	$115.40
Purchase #6	$93.61	10.302%	$103.2537	$103.25	$103.25	$103.30
Purchase #7	$124.54	5.795%	$131.7571	$131.76	$131.75	$131.80
7 purchase totals =	$741.61		$796.7341	$796.73	$796.70	$796.80