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	$37.56	6.183%	$39.8823	$39.88	$39.90	$39.90
Purchase #2	$243.57	11.220%	$270.8986	$270.90	$270.90	$270.90
Purchase #3	$54.55	10.493%	$60.2739	$60.27	$60.25	$60.30
Purchase #4	$138.59	11.596%	$154.6609	$154.66	$154.65	$154.70
Purchase #5	$89.97	9.483%	$98.5019	$98.50	$98.50	$98.50
Purchase #6	$111.32	6.568%	$118.6315	$118.63	$118.65	$118.60
Purchase #7	$13.73	11.253%	$15.275	$15.28	$15.30	$15.30
7 purchase totals =	$689.29		$758.1241	$758.12	$758.15	$758.20