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	$32.48	8.337%	$35.1879	$35.19	$35.20	$35.20
Purchase #2	$74.34	10.727%	$82.3145	$82.31	$82.30	$82.30
Purchase #3	$242.67	5.216%	$255.3277	$255.33	$255.35	$255.30
Purchase #4	$168.79	12.505%	$189.8972	$189.90	$189.90	$189.90
Purchase #5	$170.89	10.355%	$188.5857	$188.59	$188.60	$188.60
Purchase #6	$21.75	7.552%	$23.3926	$23.39	$23.40	$23.40
Purchase #7	$154.89	8.454%	$167.9844	$167.98	$168.00	$168.00
7 purchase totals =	$865.81		$942.6900	$942.69	$942.75	$942.70