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	$31.58	11.786%	$35.302	$35.30	$35.30	$35.30
Purchase #2	$133.84	7.151%	$143.4109	$143.41	$143.40	$143.40
Purchase #3	$25.56	11.791%	$28.5738	$28.57	$28.55	$28.60
Purchase #4	$77.73	5.636%	$82.1109	$82.11	$82.10	$82.10
Purchase #5	$202.57	11.649%	$226.1674	$226.17	$226.15	$226.20
Purchase #6	$80.42	12.413%	$90.4025	$90.40	$90.40	$90.40
Purchase #7	$51.48	6.749%	$54.9544	$54.95	$54.95	$55.00
7 purchase totals =	$603.18		$660.9219	$660.91	$660.85	$661.00