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	$86.82	5.818%	$91.8712	$91.87	$91.85	$91.90
Purchase #2	$172.28	4.832%	$180.6046	$180.60	$180.60	$180.60
Purchase #3	$59.62	12.867%	$67.2913	$67.29	$67.30	$67.30
Purchase #4	$100.33	9.460%	$109.8212	$109.82	$109.80	$109.80
Purchase #5	$83.25	8.133%	$90.0207	$90.02	$90.00	$90.00
Purchase #6	$32.30	13.695%	$36.7235	$36.72	$36.70	$36.70
Purchase #7	$207.41	3.220%	$214.0886	$214.09	$214.10	$214.10
7 purchase totals =	$742.01		$790.4211	$790.41	$790.35	$790.40