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	$5.49	11.781%	$6.1368	$6.14	$6.15	$6.10
Purchase #2	$215.90	6.265%	$229.4261	$229.43	$229.45	$229.40
Purchase #3	$185.52	13.801%	$211.1236	$211.12	$211.10	$211.10
Purchase #4	$91.94	10.563%	$101.6516	$101.65	$101.65	$101.70
Purchase #5	$104.27	4.834%	$109.3104	$109.31	$109.30	$109.30
Purchase #6	$71.54	12.522%	$80.4982	$80.50	$80.50	$80.50
Purchase #7	$112.73	11.142%	$125.2904	$125.29	$125.30	$125.30
7 purchase totals =	$787.39		$863.4371	$863.44	$863.45	$863.40