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	$64.74	12.682%	$72.9503	$72.95	$72.95	$73.00
Purchase #2	$105.88	3.698%	$109.7954	$109.80	$109.80	$109.80
Purchase #3	$152.77	10.167%	$168.3021	$168.30	$168.30	$168.30
Purchase #4	$197.92	13.187%	$224.0197	$224.02	$224.00	$224.00
Purchase #5	$237.88	5.131%	$250.0856	$250.09	$250.10	$250.10
Purchase #6	$59.37	9.517%	$65.0202	$65.02	$65.00	$65.00
Purchase #7	$37.50	3.120%	$38.67	$38.67	$38.65	$38.70
7 purchase totals =	$856.06		$928.8433	$928.85	$928.80	$928.90