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	$91.61	9.281%	$100.1123	$100.11	$100.10	$100.10
Purchase #2	$27.75	3.496%	$28.7201	$28.72	$28.70	$28.70
Purchase #3	$81.56	6.226%	$86.6379	$86.64	$86.65	$86.60
Purchase #4	$62.71	4.158%	$65.3175	$65.32	$65.30	$65.30
Purchase #5	$201.56	5.591%	$212.8292	$212.83	$212.85	$212.80
Purchase #6	$231.43	5.714%	$244.6539	$244.65	$244.65	$244.70
Purchase #7	$141.53	9.745%	$155.3221	$155.32	$155.30	$155.30
7 purchase totals =	$838.15		$893.5930	$893.59	$893.55	$893.50