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	$118.39	11.144%	$131.5834	$131.58	$131.60	$131.60
Purchase #2	$7.68	12.320%	$8.6262	$8.63	$8.65	$8.60
Purchase #3	$250.59	11.705%	$279.9216	$279.92	$279.90	$279.90
Purchase #4	$202.93	11.132%	$225.5202	$225.52	$225.50	$225.50
Purchase #5	$179.40	9.373%	$196.2152	$196.22	$196.20	$196.20
Purchase #6	$28.51	13.295%	$32.3004	$32.30	$32.30	$32.30
Purchase #7	$223.32	10.142%	$245.9691	$245.97	$245.95	$246.00
7 purchase totals =	$1,010.82		$1,120.1361	$1,120.14	$1,120.10	$1,120.10