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	$110.63	5.434%	$116.6416	$116.64	$116.65	$116.60
Purchase #2	$40.70	12.260%	$45.6898	$45.69	$45.70	$45.70
Purchase #3	$166.85	7.676%	$179.6574	$179.66	$179.65	$179.70
Purchase #4	$109.91	4.848%	$115.2384	$115.24	$115.25	$115.20
Purchase #5	$175.90	4.351%	$183.5534	$183.55	$183.55	$183.60
Purchase #6	$57.47	3.550%	$59.5102	$59.51	$59.50	$59.50
Purchase #7	$72.92	12.255%	$81.8563	$81.86	$81.85	$81.90
7 purchase totals =	$734.38		$782.1471	$782.15	$782.15	$782.20