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	$171.89	6.398%	$182.8875	$182.89	$182.90	$182.90
Purchase #2	$198.48	5.570%	$209.5353	$209.54	$209.55	$209.50
Purchase #3	$18.91	11.225%	$21.0326	$21.03	$21.05	$21.00
Purchase #4	$57.76	11.219%	$64.2401	$64.24	$64.25	$64.20
Purchase #5	$111.60	10.380%	$123.1841	$123.18	$123.20	$123.20
Purchase #6	$156.31	4.251%	$162.9547	$162.95	$162.95	$163.00
Purchase #7	$17.25	13.134%	$19.5156	$19.52	$19.50	$19.50
7 purchase totals =	$732.20		$783.3499	$783.35	$783.40	$783.30