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	$49.47	7.521%	$53.1906	$53.19	$53.20	$53.20
Purchase #2	$130.27	12.792%	$146.9341	$146.93	$146.95	$146.90
Purchase #3	$124.97	9.592%	$136.9571	$136.96	$136.95	$137.00
Purchase #4	$40.64	5.119%	$42.7204	$42.72	$42.70	$42.70
Purchase #5	$115.91	13.305%	$131.3318	$131.33	$131.35	$131.30
Purchase #6	$182.36	4.779%	$191.075	$191.08	$191.10	$191.10
Purchase #7	$147.25	11.656%	$164.4135	$164.41	$164.40	$164.40
7 purchase totals =	$790.87		$866.6225	$866.62	$866.65	$866.60