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	$242.88	10.351%	$268.0205	$268.02	$268.00	$268.00
Purchase #2	$61.89	11.365%	$68.9238	$68.92	$68.90	$68.90
Purchase #3	$42.86	5.764%	$45.3305	$45.33	$45.35	$45.30
Purchase #4	$196.95	13.724%	$223.9794	$223.98	$224.00	$224.00
Purchase #5	$91.33	10.700%	$101.1023	$101.10	$101.10	$101.10
Purchase #6	$37.66	6.604%	$40.1471	$40.15	$40.15	$40.10
Purchase #7	$248.38	8.592%	$269.7208	$269.72	$269.70	$269.70
7 purchase totals =	$921.95		$1,017.2244	$1,017.22	$1,017.20	$1,017.10