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	$167.37	3.334%	$172.9501	$172.95	$172.95	$173.00
Purchase #2	$56.84	13.169%	$64.3253	$64.33	$64.35	$64.30
Purchase #3	$92.78	7.770%	$99.989	$99.99	$100.00	$100.00
Purchase #4	$202.69	11.181%	$225.3528	$225.35	$225.35	$225.40
Purchase #5	$166.78	11.264%	$185.5661	$185.57	$185.55	$185.60
Purchase #6	$29.59	4.204%	$30.834	$30.83	$30.85	$30.80
Purchase #7	$226.71	5.744%	$239.7322	$239.73	$239.75	$239.70
7 purchase totals =	$942.76		$1,018.7495	$1,018.75	$1,018.80	$1,018.80