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	11.366%	$279.0164	$279.02	$279.00	$279.00
Purchase #2	$247.47	8.250%	$267.8863	$267.89	$267.90	$267.90
Purchase #3	$86.91	3.520%	$89.9692	$89.97	$89.95	$90.00
Purchase #4	$176.38	4.640%	$184.564	$184.56	$184.55	$184.60
Purchase #5	$136.97	3.178%	$141.3229	$141.32	$141.30	$141.30
Purchase #6	$8.33	4.587%	$8.7121	$8.71	$8.70	$8.70
Purchase #7	$96.56	6.846%	$103.1705	$103.17	$103.15	$103.20
7 purchase totals =	$1,003.16		$1,074.6414	$1,074.64	$1,074.55	$1,074.70