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	$52.49	5.733%	$55.4993	$55.50	$55.50	$55.50
Purchase #2	$125.80	7.247%	$134.9167	$134.92	$134.90	$134.90
Purchase #3	$217.68	7.264%	$233.4923	$233.49	$233.50	$233.50
Purchase #4	$232.79	13.460%	$264.1235	$264.12	$264.10	$264.10
Purchase #5	$166.93	9.342%	$182.5246	$182.52	$182.50	$182.50
Purchase #6	$79.52	13.784%	$90.481	$90.48	$90.50	$90.50
Purchase #7	$222.32	9.599%	$243.6605	$243.66	$243.65	$243.70
7 purchase totals =	$1,097.53		$1,204.6979	$1,204.69	$1,204.65	$1,204.70