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	$114.54	7.472%	$123.0984	$123.10	$123.10	$123.10
Purchase #2	$26.74	3.401%	$27.6494	$27.65	$27.65	$27.60
Purchase #3	$145.41	7.803%	$156.7563	$156.76	$156.75	$156.80
Purchase #4	$78.42	13.752%	$89.2043	$89.20	$89.20	$89.20
Purchase #5	$172.54	3.758%	$179.0241	$179.02	$179.00	$179.00
Purchase #6	$188.86	13.168%	$213.7291	$213.73	$213.75	$213.70
Purchase #7	$36.27	10.453%	$40.0613	$40.06	$40.05	$40.10
7 purchase totals =	$762.78		$829.5229	$829.52	$829.50	$829.50