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	$80.39	10.808%	$89.0786	$89.08	$89.10	$89.10
Purchase #2	$84.27	4.543%	$88.0984	$88.10	$88.10	$88.10
Purchase #3	$67.50	8.379%	$73.1558	$73.16	$73.15	$73.20
Purchase #4	$207.63	7.224%	$222.6292	$222.63	$222.65	$222.60
Purchase #5	$200.83	5.841%	$212.5605	$212.56	$212.55	$212.60
Purchase #6	$146.51	11.206%	$162.9279	$162.93	$162.95	$162.90
Purchase #7	$28.67	11.745%	$32.0373	$32.04	$32.05	$32.00
7 purchase totals =	$815.80		$880.4877	$880.50	$880.55	$880.50