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	$29.57	4.689%	$30.9565	$30.96	$30.95	$31.00
Purchase #2	$99.73	12.584%	$112.28	$112.28	$112.30	$112.30
Purchase #3	$27.84	9.841%	$30.5797	$30.58	$30.60	$30.60
Purchase #4	$25.33	11.821%	$28.3243	$28.32	$28.30	$28.30
Purchase #5	$90.92	11.546%	$101.4176	$101.42	$101.40	$101.40
Purchase #6	$40.95	13.654%	$46.5413	$46.54	$46.55	$46.50
Purchase #7	$105.72	3.664%	$109.5936	$109.59	$109.60	$109.60
7 purchase totals =	$420.06		$459.6930	$459.69	$459.70	$459.70