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	$142.76	9.263%	$155.9839	$155.98	$156.00	$156.00
Purchase #2	$41.95	10.399%	$46.3124	$46.31	$46.30	$46.30
Purchase #3	$65.29	5.482%	$68.8692	$68.87	$68.85	$68.90
Purchase #4	$59.84	11.675%	$66.8263	$66.83	$66.85	$66.80
Purchase #5	$78.26	10.538%	$86.507	$86.51	$86.50	$86.50
Purchase #6	$213.85	13.776%	$243.31	$243.31	$243.30	$243.30
Purchase #7	$93.59	11.193%	$104.0655	$104.07	$104.05	$104.10
7 purchase totals =	$695.54		$771.8743	$771.88	$771.85	$771.90