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	$25.55	10.688%	$28.2808	$28.28	$28.30	$28.30
Purchase #2	$101.37	4.352%	$105.7816	$105.78	$105.80	$105.80
Purchase #3	$212.85	12.271%	$238.9688	$238.97	$238.95	$239.00
Purchase #4	$60.52	7.134%	$64.8375	$64.84	$64.85	$64.80
Purchase #5	$97.46	12.584%	$109.7244	$109.72	$109.70	$109.70
Purchase #6	$243.52	8.552%	$264.3458	$264.35	$264.35	$264.30
Purchase #7	$93.91	6.416%	$99.9353	$99.94	$99.95	$99.90
7 purchase totals =	$835.18		$911.8742	$911.88	$911.90	$911.80