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	$9.27	11.597%	$10.345	$10.35	$10.35	$10.30
Purchase #2	$68.60	13.726%	$78.016	$78.02	$78.00	$78.00
Purchase #3	$24.67	12.751%	$27.8157	$27.82	$27.80	$27.80
Purchase #4	$250.25	5.837%	$264.8571	$264.86	$264.85	$264.90
Purchase #5	$37.51	12.355%	$42.1444	$42.14	$42.15	$42.10
Purchase #6	$211.33	10.331%	$233.1625	$233.16	$233.15	$233.20
Purchase #7	$135.30	12.707%	$152.4926	$152.49	$152.50	$152.50
7 purchase totals =	$736.93		$808.8333	$808.84	$808.80	$808.80