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	$206.33	3.180%	$212.8913	$212.89	$212.90	$212.90
Purchase #2	$95.46	8.114%	$103.2056	$103.21	$103.20	$103.20
Purchase #3	$155.69	13.401%	$176.554	$176.55	$176.55	$176.60
Purchase #4	$231.69	10.115%	$255.1254	$255.13	$255.15	$255.10
Purchase #5	$116.30	12.146%	$130.4258	$130.43	$130.45	$130.40
Purchase #6	$167.61	6.690%	$178.8231	$178.82	$178.80	$178.80
Purchase #7	$30.76	9.373%	$33.6431	$33.64	$33.65	$33.60
7 purchase totals =	$1,003.84		$1,090.6683	$1,090.67	$1,090.70	$1,090.60