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	$70.31	10.427%	$77.6412	$77.64	$77.65	$77.60
Purchase #2	$191.46	6.730%	$204.3453	$204.35	$204.35	$204.30
Purchase #3	$79.73	12.196%	$89.4539	$89.45	$89.45	$89.50
Purchase #4	$19.79	11.126%	$21.9918	$21.99	$22.00	$22.00
Purchase #5	$170.97	8.467%	$185.446	$185.45	$185.45	$185.40
Purchase #6	$93.81	7.174%	$100.5399	$100.54	$100.55	$100.50
Purchase #7	$170.52	4.678%	$178.4969	$178.50	$178.50	$178.50
7 purchase totals =	$796.59		$857.9150	$857.92	$857.95	$857.80