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	$34.78	8.702%	$37.8066	$37.81	$37.80	$37.80
Purchase #2	$182.54	6.403%	$194.228	$194.23	$194.25	$194.20
Purchase #3	$94.41	5.245%	$99.3618	$99.36	$99.35	$99.40
Purchase #4	$127.90	13.261%	$144.8608	$144.86	$144.85	$144.90
Purchase #5	$66.58	4.764%	$69.7519	$69.75	$69.75	$69.80
Purchase #6	$82.38	3.309%	$85.106	$85.11	$85.10	$85.10
Purchase #7	$104.88	8.135%	$113.412	$113.41	$113.40	$113.40
7 purchase totals =	$693.47		$744.5271	$744.53	$744.50	$744.60