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	$76.48	11.586%	$85.341	$85.34	$85.35	$85.30
Purchase #2	$173.60	3.441%	$179.5736	$179.57	$179.55	$179.60
Purchase #3	$80.91	10.592%	$89.48	$89.48	$89.50	$89.50
Purchase #4	$79.37	9.850%	$87.1879	$87.19	$87.20	$87.20
Purchase #5	$21.27	4.245%	$22.1729	$22.17	$22.15	$22.20
Purchase #6	$198.38	10.111%	$218.4382	$218.44	$218.45	$218.40
Purchase #7	$40.60	3.841%	$42.1594	$42.16	$42.15	$42.20
7 purchase totals =	$670.61		$724.3530	$724.35	$724.35	$724.40