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	$56.90	7.750%	$61.3098	$61.31	$61.30	$61.30
Purchase #2	$201.89	13.361%	$228.8645	$228.86	$228.85	$228.90
Purchase #3	$250.33	5.786%	$264.8141	$264.81	$264.80	$264.80
Purchase #4	$130.96	8.711%	$142.3679	$142.37	$142.35	$142.40
Purchase #5	$55.66	11.566%	$62.0976	$62.10	$62.10	$62.10
Purchase #6	$128.67	3.862%	$133.6392	$133.64	$133.65	$133.60
Purchase #7	$234.31	6.209%	$248.8583	$248.86	$248.85	$248.90
7 purchase totals =	$1,058.72		$1,141.9514	$1,141.95	$1,141.90	$1,142.00