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	$52.27	10.755%	$57.8916	$57.89	$57.90	$57.90
Purchase #2	$247.40	10.678%	$273.8174	$273.82	$273.80	$273.80
Purchase #3	$159.66	8.132%	$172.6436	$172.64	$172.65	$172.60
Purchase #4	$16.65	10.371%	$18.3768	$18.38	$18.40	$18.40
Purchase #5	$95.78	5.290%	$100.8468	$100.85	$100.85	$100.80
Purchase #6	$41.99	3.133%	$43.3055	$43.31	$43.30	$43.30
Purchase #7	$113.98	3.126%	$117.543	$117.54	$117.55	$117.50
7 purchase totals =	$727.73		$784.4247	$784.43	$784.45	$784.30