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	$171.48	5.156%	$180.3215	$180.32	$180.30	$180.30
Purchase #2	$217.95	11.224%	$242.4127	$242.41	$242.40	$242.40
Purchase #3	$155.31	10.759%	$172.0198	$172.02	$172.00	$172.00
Purchase #4	$14.83	10.164%	$16.3373	$16.34	$16.35	$16.30
Purchase #5	$240.86	10.360%	$265.8131	$265.81	$265.80	$265.80
Purchase #6	$26.25	7.566%	$28.2361	$28.24	$28.25	$28.20
Purchase #7	$59.35	3.690%	$61.54	$61.54	$61.55	$61.50
7 purchase totals =	$886.03		$966.6805	$966.68	$966.65	$966.50