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	$166.35	7.197%	$178.3222	$178.32	$178.30	$178.30
Purchase #2	$81.50	6.453%	$86.7592	$86.76	$86.75	$86.80
Purchase #3	$165.42	3.468%	$171.1568	$171.16	$171.15	$171.20
Purchase #4	$17.41	5.570%	$18.3797	$18.38	$18.40	$18.40
Purchase #5	$43.56	10.775%	$48.2536	$48.25	$48.25	$48.30
Purchase #6	$127.54	7.740%	$137.4116	$137.41	$137.40	$137.40
Purchase #7	$121.66	11.802%	$136.0183	$136.02	$136.00	$136.00
7 purchase totals =	$723.44		$776.3014	$776.30	$776.25	$776.40