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	$250.54	11.610%	$279.6277	$279.63	$279.65	$279.60
Purchase #2	$152.78	12.815%	$172.3588	$172.36	$172.35	$172.40
Purchase #3	$99.69	13.300%	$112.9488	$112.95	$112.95	$112.90
Purchase #4	$185.50	11.782%	$207.3556	$207.36	$207.35	$207.40
Purchase #5	$131.93	7.297%	$141.5569	$141.56	$141.55	$141.60
Purchase #6	$67.75	13.142%	$76.6537	$76.65	$76.65	$76.70
Purchase #7	$43.48	4.406%	$45.3957	$45.40	$45.40	$45.40
7 purchase totals =	$931.67		$1,035.8972	$1,035.91	$1,035.90	$1,036.00