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	$115.36	13.579%	$131.0247	$131.02	$131.00	$131.00
Purchase #2	$34.36	4.327%	$35.8468	$35.85	$35.85	$35.80
Purchase #3	$136.78	4.740%	$143.2634	$143.26	$143.25	$143.30
Purchase #4	$184.59	6.519%	$196.6234	$196.62	$196.60	$196.60
Purchase #5	$136.54	4.745%	$143.0188	$143.02	$143.00	$143.00
Purchase #6	$96.51	5.562%	$101.8779	$101.88	$101.90	$101.90
Purchase #7	$212.63	12.125%	$238.4114	$238.41	$238.40	$238.40
7 purchase totals =	$916.77		$990.0664	$990.06	$990.00	$990.00