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	$88.70	13.585%	$100.7499	$100.75	$100.75	$100.70
Purchase #2	$94.43	7.372%	$101.3914	$101.39	$101.40	$101.40
Purchase #3	$36.39	6.162%	$38.6324	$38.63	$38.65	$38.60
Purchase #4	$210.80	3.858%	$218.9327	$218.93	$218.95	$218.90
Purchase #5	$247.38	11.328%	$275.4032	$275.40	$275.40	$275.40
Purchase #6	$34.92	6.376%	$37.1465	$37.15	$37.15	$37.10
Purchase #7	$212.42	3.802%	$220.4962	$220.50	$220.50	$220.50
7 purchase totals =	$925.04		$992.7523	$992.75	$992.80	$992.60