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	$8.61	11.300%	$9.5829	$9.58	$9.60	$9.60
Purchase #2	$111.31	12.847%	$125.61	$125.61	$125.60	$125.60
Purchase #3	$209.57	12.300%	$235.3471	$235.35	$235.35	$235.30
Purchase #4	$132.37	7.507%	$142.307	$142.31	$142.30	$142.30
Purchase #5	$114.97	11.533%	$128.2295	$128.23	$128.25	$128.20
Purchase #6	$84.54	5.566%	$89.2455	$89.25	$89.25	$89.20
Purchase #7	$159.40	3.704%	$165.3042	$165.30	$165.30	$165.30
7 purchase totals =	$820.77		$895.6262	$895.63	$895.65	$895.50