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	$57.34	6.728%	$61.1978	$61.20	$61.20	$61.20
Purchase #2	$218.26	11.855%	$244.1347	$244.13	$244.15	$244.10
Purchase #3	$94.63	6.544%	$100.8226	$100.82	$100.80	$100.80
Purchase #4	$115.71	9.158%	$126.3067	$126.31	$126.30	$126.30
Purchase #5	$115.36	6.839%	$123.2495	$123.25	$123.25	$123.20
Purchase #6	$16.72	9.687%	$18.3397	$18.34	$18.35	$18.30
Purchase #7	$43.56	10.682%	$48.2131	$48.21	$48.20	$48.20
7 purchase totals =	$661.58		$722.2641	$722.26	$722.25	$722.10