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	$73.47	5.322%	$77.3801	$77.38	$77.40	$77.40
Purchase #2	$67.38	10.582%	$74.5102	$74.51	$74.50	$74.50
Purchase #3	$99.93	6.660%	$106.5853	$106.59	$106.60	$106.60
Purchase #4	$218.93	11.411%	$243.9121	$243.91	$243.90	$243.90
Purchase #5	$247.86	12.812%	$279.6158	$279.62	$279.60	$279.60
Purchase #6	$90.63	11.239%	$100.8159	$100.82	$100.80	$100.80
Purchase #7	$125.50	6.372%	$133.4969	$133.50	$133.50	$133.50
7 purchase totals =	$923.70		$1,016.3163	$1,016.33	$1,016.30	$1,016.30