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	$115.69	6.521%	$123.2341	$123.23	$123.25	$123.20
Purchase #2	$50.62	9.532%	$55.4451	$55.45	$55.45	$55.40
Purchase #3	$133.62	11.746%	$149.315	$149.32	$149.30	$149.30
Purchase #4	$83.94	8.179%	$90.8055	$90.81	$90.80	$90.80
Purchase #5	$167.73	3.425%	$173.4748	$173.47	$173.45	$173.50
Purchase #6	$59.48	13.424%	$67.4646	$67.46	$67.45	$67.50
Purchase #7	$191.35	3.489%	$198.0262	$198.03	$198.05	$198.00
7 purchase totals =	$802.43		$857.7653	$857.77	$857.75	$857.70