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	$56.40	6.247%	$59.9233	$59.92	$59.90	$59.90
Purchase #2	$65.41	8.212%	$70.7815	$70.78	$70.80	$70.80
Purchase #3	$82.65	11.761%	$92.3705	$92.37	$92.35	$92.40
Purchase #4	$243.59	4.633%	$254.8755	$254.88	$254.90	$254.90
Purchase #5	$198.30	6.840%	$211.8637	$211.86	$211.85	$211.90
Purchase #6	$19.28	11.614%	$21.5192	$21.52	$21.50	$21.50
Purchase #7	$135.62	12.362%	$152.3853	$152.39	$152.40	$152.40
7 purchase totals =	$801.25		$863.7190	$863.72	$863.70	$863.80