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	$241.57	4.106%	$251.4889	$251.49	$251.50	$251.50
Purchase #2	$37.29	9.508%	$40.8355	$40.84	$40.85	$40.80
Purchase #3	$195.27	13.348%	$221.3346	$221.33	$221.35	$221.30
Purchase #4	$94.36	4.802%	$98.8912	$98.89	$98.90	$98.90
Purchase #5	$233.34	6.815%	$249.2421	$249.24	$249.25	$249.20
Purchase #6	$38.83	6.784%	$41.4642	$41.46	$41.45	$41.50
Purchase #7	$247.63	8.314%	$268.218	$268.22	$268.20	$268.20
7 purchase totals =	$1,088.29		$1,171.4745	$1,171.47	$1,171.50	$1,171.40