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	$25.27	8.313%	$27.3707	$27.37	$27.35	$27.40
Purchase #2	$169.98	6.199%	$180.5171	$180.52	$180.50	$180.50
Purchase #3	$11.71	10.378%	$12.9253	$12.93	$12.95	$12.90
Purchase #4	$191.61	3.282%	$197.8986	$197.90	$197.90	$197.90
Purchase #5	$90.82	9.126%	$99.1082	$99.11	$99.10	$99.10
Purchase #6	$68.73	3.186%	$70.9197	$70.92	$70.90	$70.90
Purchase #7	$11.51	9.734%	$12.6304	$12.63	$12.65	$12.60
7 purchase totals =	$569.63		$601.3700	$601.38	$601.35	$601.30