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	$64.41	10.390%	$71.1022	$71.10	$71.10	$71.10
Purchase #2	$179.74	3.129%	$185.3641	$185.36	$185.35	$185.40
Purchase #3	$196.50	10.200%	$216.543	$216.54	$216.55	$216.50
Purchase #4	$56.93	7.792%	$61.366	$61.37	$61.35	$61.40
Purchase #5	$135.49	10.500%	$149.7165	$149.72	$149.70	$149.70
Purchase #6	$216.55	7.742%	$233.3153	$233.32	$233.30	$233.30
Purchase #7	$91.57	9.356%	$100.1373	$100.14	$100.15	$100.10
7 purchase totals =	$941.19		$1,017.5444	$1,017.55	$1,017.50	$1,017.50