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	$44.88	12.774%	$50.613	$50.61	$50.60	$50.60
Purchase #2	$139.33	9.400%	$152.427	$152.43	$152.45	$152.40
Purchase #3	$141.52	7.529%	$152.175	$152.18	$152.20	$152.20
Purchase #4	$111.36	8.333%	$120.6396	$120.64	$120.65	$120.60
Purchase #5	$127.97	11.111%	$142.1887	$142.19	$142.20	$142.20
Purchase #6	$136.43	13.761%	$155.2041	$155.20	$155.20	$155.20
Purchase #7	$52.27	12.592%	$58.8518	$58.85	$58.85	$58.90
7 purchase totals =	$753.76		$832.0992	$832.10	$832.15	$832.10