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	$80.76	9.341%	$88.3038	$88.30	$88.30	$88.30
Purchase #2	$125.51	3.159%	$129.4749	$129.47	$129.45	$129.50
Purchase #3	$191.25	6.581%	$203.8362	$203.84	$203.85	$203.80
Purchase #4	$38.94	10.758%	$43.1292	$43.13	$43.15	$43.10
Purchase #5	$30.54	4.404%	$31.885	$31.89	$31.90	$31.90
Purchase #6	$73.49	7.321%	$78.8702	$78.87	$78.85	$78.90
Purchase #7	$55.30	11.686%	$61.7624	$61.76	$61.75	$61.80
7 purchase totals =	$595.79		$637.2617	$637.26	$637.25	$637.30