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	$169.81	5.520%	$179.1835	$179.18	$179.20	$179.20
Purchase #2	$115.64	13.558%	$131.3185	$131.32	$131.30	$131.30
Purchase #3	$246.41	9.460%	$269.7204	$269.72	$269.70	$269.70
Purchase #4	$48.83	11.838%	$54.6105	$54.61	$54.60	$54.60
Purchase #5	$232.55	7.814%	$250.7215	$250.72	$250.70	$250.70
Purchase #6	$58.86	5.805%	$62.2768	$62.28	$62.30	$62.30
Purchase #7	$36.28	6.698%	$38.71	$38.71	$38.70	$38.70
7 purchase totals =	$908.38		$986.5412	$986.54	$986.50	$986.50