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	$88.99	12.148%	$99.8005	$99.80	$99.80	$99.80
Purchase #2	$101.56	10.199%	$111.9181	$111.92	$111.90	$111.90
Purchase #3	$196.38	4.584%	$205.3821	$205.38	$205.40	$205.40
Purchase #4	$39.53	6.538%	$42.1145	$42.11	$42.10	$42.10
Purchase #5	$175.68	9.593%	$192.533	$192.53	$192.55	$192.50
Purchase #6	$144.40	8.827%	$157.1462	$157.15	$157.15	$157.10
Purchase #7	$176.75	10.222%	$194.8174	$194.82	$194.80	$194.80
7 purchase totals =	$923.29		$1,003.7118	$1,003.71	$1,003.70	$1,003.60