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	$243.43	9.870%	$267.4565	$267.46	$267.45	$267.50
Purchase #2	$227.66	10.559%	$251.6986	$251.70	$251.70	$251.70
Purchase #3	$223.86	11.828%	$250.3382	$250.34	$250.35	$250.30
Purchase #4	$112.33	7.847%	$121.1445	$121.14	$121.15	$121.10
Purchase #5	$209.71	6.768%	$223.9032	$223.90	$223.90	$223.90
Purchase #6	$134.31	13.378%	$152.278	$152.28	$152.30	$152.30
Purchase #7	$59.55	12.713%	$67.1206	$67.12	$67.10	$67.10
7 purchase totals =	$1,210.85		$1,333.9396	$1,333.94	$1,333.95	$1,333.90