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	$210.61	5.826%	$222.8801	$222.88	$222.90	$222.90
Purchase #2	$108.60	11.322%	$120.8957	$120.90	$120.90	$120.90
Purchase #3	$26.87	12.225%	$30.1549	$30.15	$30.15	$30.20
Purchase #4	$72.72	13.614%	$82.6201	$82.62	$82.60	$82.60
Purchase #5	$104.41	13.649%	$118.6609	$118.66	$118.65	$118.70
Purchase #6	$57.89	11.281%	$64.4206	$64.42	$64.40	$64.40
Purchase #7	$165.34	10.858%	$183.2926	$183.29	$183.30	$183.30
7 purchase totals =	$746.44		$822.9249	$822.92	$822.90	$823.00