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	$74.51	5.430%	$78.5559	$78.56	$78.55	$78.60
Purchase #2	$29.49	3.544%	$30.5351	$30.54	$30.55	$30.50
Purchase #3	$166.57	11.597%	$185.8871	$185.89	$185.90	$185.90
Purchase #4	$223.47	4.770%	$234.1295	$234.13	$234.15	$234.10
Purchase #5	$126.85	8.127%	$137.1591	$137.16	$137.15	$137.20
Purchase #6	$185.94	7.299%	$199.5118	$199.51	$199.50	$199.50
Purchase #7	$245.33	9.305%	$268.158	$268.16	$268.15	$268.20
7 purchase totals =	$1,052.16		$1,133.9365	$1,133.95	$1,133.95	$1,134.00