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	$75.91	3.239%	$78.3687	$78.37	$78.35	$78.40
Purchase #2	$33.93	10.736%	$37.5727	$37.57	$37.55	$37.60
Purchase #3	$88.60	13.131%	$100.2341	$100.23	$100.25	$100.20
Purchase #4	$202.29	13.312%	$229.2188	$229.22	$229.20	$229.20
Purchase #5	$188.40	6.331%	$200.3276	$200.33	$200.35	$200.30
Purchase #6	$229.80	10.121%	$253.0581	$253.06	$253.05	$253.10
Purchase #7	$84.82	10.847%	$94.0204	$94.02	$94.00	$94.00
7 purchase totals =	$903.75		$992.8004	$992.80	$992.75	$992.80