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	$30.68	9.652%	$33.6412	$33.64	$33.65	$33.60
Purchase #2	$173.25	9.743%	$190.1297	$190.13	$190.15	$190.10
Purchase #3	$89.26	11.437%	$99.4687	$99.47	$99.45	$99.50
Purchase #4	$213.95	7.755%	$230.5418	$230.54	$230.55	$230.50
Purchase #5	$135.59	12.121%	$152.0249	$152.02	$152.00	$152.00
Purchase #6	$42.83	10.611%	$47.3747	$47.37	$47.35	$47.40
Purchase #7	$42.79	7.387%	$45.9509	$45.95	$45.95	$46.00
7 purchase totals =	$728.35		$799.1319	$799.12	$799.10	$799.10