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	$178.75	4.575%	$186.9278	$186.93	$186.95	$186.90
Purchase #2	$30.33	11.796%	$33.9077	$33.91	$33.90	$33.90
Purchase #3	$217.41	10.447%	$240.1228	$240.12	$240.10	$240.10
Purchase #4	$130.50	7.517%	$140.3097	$140.31	$140.30	$140.30
Purchase #5	$133.88	6.800%	$142.9838	$142.98	$143.00	$143.00
Purchase #6	$166.80	12.654%	$187.9069	$187.91	$187.90	$187.90
Purchase #7	$62.51	13.236%	$70.7838	$70.78	$70.80	$70.80
7 purchase totals =	$920.18		$1,002.9425	$1,002.94	$1,002.95	$1,002.90