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	$124.41	13.537%	$141.2514	$141.25	$141.25	$141.30
Purchase #2	$237.63	13.454%	$269.6007	$269.60	$269.60	$269.60
Purchase #3	$129.98	8.712%	$141.3039	$141.30	$141.30	$141.30
Purchase #4	$109.62	3.814%	$113.8009	$113.80	$113.80	$113.80
Purchase #5	$235.86	10.178%	$259.8658	$259.87	$259.85	$259.90
Purchase #6	$80.74	10.329%	$89.0796	$89.08	$89.10	$89.10
Purchase #7	$37.34	4.748%	$39.1129	$39.11	$39.10	$39.10
7 purchase totals =	$955.58		$1,054.0152	$1,054.01	$1,054.00	$1,054.10