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	$162.30	10.280%	$178.9844	$178.98	$179.00	$179.00
Purchase #2	$68.76	5.266%	$72.3809	$72.38	$72.40	$72.40
Purchase #3	$183.77	4.177%	$191.4461	$191.45	$191.45	$191.40
Purchase #4	$60.32	9.238%	$65.8924	$65.89	$65.90	$65.90
Purchase #5	$47.36	11.814%	$52.9551	$52.96	$52.95	$53.00
Purchase #6	$185.50	8.674%	$201.5903	$201.59	$201.60	$201.60
Purchase #7	$118.39	7.432%	$127.1887	$127.19	$127.20	$127.20
7 purchase totals =	$826.40		$890.4379	$890.44	$890.50	$890.50