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	$45.78	13.403%	$51.9159	$51.92	$51.90	$51.90
Purchase #2	$67.85	5.240%	$71.4053	$71.41	$71.40	$71.40
Purchase #3	$250.98	4.799%	$263.0245	$263.02	$263.00	$263.00
Purchase #4	$94.47	10.236%	$104.1399	$104.14	$104.15	$104.10
Purchase #5	$198.68	11.294%	$221.1189	$221.12	$221.10	$221.10
Purchase #6	$111.26	10.578%	$123.0291	$123.03	$123.05	$123.00
Purchase #7	$248.48	5.305%	$261.6619	$261.66	$261.65	$261.70
7 purchase totals =	$1,017.50		$1,096.2955	$1,096.30	$1,096.25	$1,096.20