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	$100.26	9.315%	$109.5992	$109.60	$109.60	$109.60
Purchase #2	$231.69	11.405%	$258.1142	$258.11	$258.10	$258.10
Purchase #3	$141.96	11.689%	$158.5537	$158.55	$158.55	$158.60
Purchase #4	$84.95	7.862%	$91.6288	$91.63	$91.65	$91.60
Purchase #5	$73.74	4.212%	$76.8459	$76.85	$76.85	$76.80
Purchase #6	$85.60	12.457%	$96.2632	$96.26	$96.25	$96.30
Purchase #7	$70.54	13.173%	$79.8322	$79.83	$79.85	$79.80
7 purchase totals =	$788.74		$870.8372	$870.83	$870.85	$870.80