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	$28.67	13.471%	$32.5321	$32.53	$32.55	$32.50
Purchase #2	$100.74	12.327%	$113.1582	$113.16	$113.15	$113.20
Purchase #3	$61.36	4.509%	$64.1267	$64.13	$64.15	$64.10
Purchase #4	$31.27	4.729%	$32.7488	$32.75	$32.75	$32.70
Purchase #5	$125.53	11.456%	$139.9107	$139.91	$139.90	$139.90
Purchase #6	$153.83	11.571%	$171.6297	$171.63	$171.65	$171.60
Purchase #7	$248.54	10.150%	$273.7668	$273.77	$273.75	$273.80
7 purchase totals =	$749.94		$827.8730	$827.88	$827.90	$827.80