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	$33.70	9.272%	$36.8247	$36.82	$36.80	$36.80
Purchase #2	$47.89	9.150%	$52.2719	$52.27	$52.25	$52.30
Purchase #3	$93.50	6.758%	$99.8187	$99.82	$99.80	$99.80
Purchase #4	$241.70	13.833%	$275.1344	$275.13	$275.15	$275.10
Purchase #5	$162.69	12.131%	$182.4259	$182.43	$182.45	$182.40
Purchase #6	$165.73	6.206%	$176.0152	$176.02	$176.00	$176.00
Purchase #7	$231.50	7.671%	$249.2584	$249.26	$249.25	$249.30
7 purchase totals =	$976.71		$1,071.7492	$1,071.75	$1,071.70	$1,071.70