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	$206.42	12.334%	$231.8798	$231.88	$231.90	$231.90
Purchase #2	$111.81	7.809%	$120.5412	$120.54	$120.55	$120.50
Purchase #3	$236.73	8.217%	$256.1821	$256.18	$256.20	$256.20
Purchase #4	$34.94	12.748%	$39.3942	$39.39	$39.40	$39.40
Purchase #5	$157.98	10.150%	$174.015	$174.02	$174.00	$174.00
Purchase #6	$82.56	6.658%	$88.0568	$88.06	$88.05	$88.10
Purchase #7	$170.32	11.240%	$189.464	$189.46	$189.45	$189.50
7 purchase totals =	$1,000.76		$1,099.5331	$1,099.53	$1,099.55	$1,099.60