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	$34.54	12.702%	$38.9273	$38.93	$38.95	$38.90
Purchase #2	$98.93	10.470%	$109.288	$109.29	$109.30	$109.30
Purchase #3	$102.36	9.304%	$111.8836	$111.88	$111.90	$111.90
Purchase #4	$73.42	12.197%	$82.375	$82.38	$82.40	$82.40
Purchase #5	$46.66	13.411%	$52.9176	$52.92	$52.90	$52.90
Purchase #6	$125.43	8.712%	$136.3575	$136.36	$136.35	$136.40
Purchase #7	$142.38	8.653%	$154.7001	$154.70	$154.70	$154.70
7 purchase totals =	$623.72		$686.4491	$686.46	$686.50	$686.50