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	$51.81	3.870%	$53.815	$53.82	$53.80	$53.80
Purchase #2	$143.71	4.465%	$150.1267	$150.13	$150.15	$150.10
Purchase #3	$35.71	4.662%	$37.3748	$37.37	$37.35	$37.40
Purchase #4	$137.36	7.438%	$147.5768	$147.58	$147.60	$147.60
Purchase #5	$83.69	6.175%	$88.8579	$88.86	$88.85	$88.90
Purchase #6	$228.85	8.812%	$249.0163	$249.02	$249.00	$249.00
Purchase #7	$35.38	13.668%	$40.2157	$40.22	$40.20	$40.20
7 purchase totals =	$716.51		$766.9832	$767.00	$766.95	$767.00