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	$179.42	13.432%	$203.5197	$203.52	$203.50	$203.50
Purchase #2	$51.46	4.813%	$53.9368	$53.94	$53.95	$53.90
Purchase #3	$138.42	10.191%	$152.5264	$152.53	$152.55	$152.50
Purchase #4	$222.31	11.522%	$247.9246	$247.92	$247.90	$247.90
Purchase #5	$84.76	8.167%	$91.6823	$91.68	$91.70	$91.70
Purchase #6	$139.67	7.454%	$150.081	$150.08	$150.10	$150.10
Purchase #7	$54.64	12.527%	$61.4848	$61.48	$61.50	$61.50
7 purchase totals =	$870.68		$961.1556	$961.15	$961.20	$961.10