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	$36.33	9.636%	$39.8308	$39.83	$39.85	$39.80
Purchase #2	$148.99	7.290%	$159.8514	$159.85	$159.85	$159.90
Purchase #3	$131.78	9.505%	$144.3057	$144.31	$144.30	$144.30
Purchase #4	$91.71	3.251%	$94.6915	$94.69	$94.70	$94.70
Purchase #5	$91.76	12.744%	$103.4539	$103.45	$103.45	$103.50
Purchase #6	$57.55	7.560%	$61.9008	$61.90	$61.90	$61.90
Purchase #7	$169.49	6.681%	$180.8136	$180.81	$180.80	$180.80
7 purchase totals =	$727.61		$784.8477	$784.84	$784.85	$784.90