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	$27.56	3.382%	$28.4921	$28.49	$28.50	$28.50
Purchase #2	$80.77	11.843%	$90.3356	$90.34	$90.35	$90.30
Purchase #3	$127.33	12.805%	$143.6346	$143.63	$143.65	$143.60
Purchase #4	$180.59	6.425%	$192.1929	$192.19	$192.20	$192.20
Purchase #5	$230.39	4.385%	$240.4926	$240.49	$240.50	$240.50
Purchase #6	$96.83	4.660%	$101.3423	$101.34	$101.35	$101.30
Purchase #7	$56.74	6.184%	$60.2488	$60.25	$60.25	$60.20
7 purchase totals =	$800.21		$856.7389	$856.73	$856.80	$856.60