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	$55.41	9.263%	$60.5426	$60.54	$60.55	$60.50
Purchase #2	$172.88	10.456%	$190.9563	$190.96	$190.95	$191.00
Purchase #3	$82.30	10.344%	$90.8131	$90.81	$90.80	$90.80
Purchase #4	$110.68	12.200%	$124.183	$124.18	$124.20	$124.20
Purchase #5	$234.50	10.486%	$259.0897	$259.09	$259.10	$259.10
Purchase #6	$117.25	12.173%	$131.5228	$131.52	$131.50	$131.50
Purchase #7	$132.72	13.112%	$150.1222	$150.12	$150.10	$150.10
7 purchase totals =	$905.74		$1,007.2297	$1,007.22	$1,007.20	$1,007.20