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	$192.52	11.316%	$214.3056	$214.31	$214.30	$214.30
Purchase #2	$96.25	7.280%	$103.257	$103.26	$103.25	$103.30
Purchase #3	$80.59	7.588%	$86.7052	$86.71	$86.70	$86.70
Purchase #4	$199.80	11.761%	$223.2985	$223.30	$223.30	$223.30
Purchase #5	$19.28	3.742%	$20.0015	$20.00	$20.00	$20.00
Purchase #6	$184.36	6.442%	$196.2365	$196.24	$196.25	$196.20
Purchase #7	$129.90	3.859%	$134.9128	$134.91	$134.90	$134.90
7 purchase totals =	$902.70		$978.7171	$978.73	$978.70	$978.70