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	$48.83	3.474%	$50.5264	$50.53	$50.55	$50.50
Purchase #2	$24.82	13.645%	$28.2067	$28.21	$28.20	$28.20
Purchase #3	$143.50	13.438%	$162.7835	$162.78	$162.80	$162.80
Purchase #4	$179.50	9.682%	$196.8792	$196.88	$196.90	$196.90
Purchase #5	$196.87	7.106%	$210.8596	$210.86	$210.85	$210.90
Purchase #6	$165.91	7.343%	$178.0928	$178.09	$178.10	$178.10
Purchase #7	$146.51	9.784%	$160.8445	$160.84	$160.85	$160.80
7 purchase totals =	$905.94		$988.1927	$988.19	$988.25	$988.20