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	$127.54	11.334%	$141.9954	$142.00	$142.00	$142.00
Purchase #2	$176.74	6.138%	$187.5883	$187.59	$187.60	$187.60
Purchase #3	$81.69	7.791%	$88.0545	$88.05	$88.05	$88.10
Purchase #4	$17.65	3.774%	$18.3161	$18.32	$18.30	$18.30
Purchase #5	$56.56	13.380%	$64.1277	$64.13	$64.15	$64.10
Purchase #6	$35.37	13.607%	$40.1828	$40.18	$40.20	$40.20
Purchase #7	$62.91	11.102%	$69.8943	$69.89	$69.90	$69.90
7 purchase totals =	$558.46		$610.1591	$610.16	$610.20	$610.20