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	$21.51	4.245%	$22.4231	$22.42	$22.40	$22.40
Purchase #2	$174.59	12.728%	$196.8118	$196.81	$196.80	$196.80
Purchase #3	$66.26	9.816%	$72.7641	$72.76	$72.75	$72.80
Purchase #4	$231.28	4.159%	$240.8989	$240.90	$240.90	$240.90
Purchase #5	$111.91	4.498%	$116.9437	$116.94	$116.95	$116.90
Purchase #6	$186.30	7.312%	$199.9223	$199.92	$199.90	$199.90
Purchase #7	$188.71	6.145%	$200.3062	$200.31	$200.30	$200.30
7 purchase totals =	$980.56		$1,050.0701	$1,050.06	$1,050.00	$1,050.00