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	$115.41	6.834%	$123.2971	$123.30	$123.30	$123.30
Purchase #2	$135.53	7.599%	$145.8289	$145.83	$145.85	$145.80
Purchase #3	$144.84	5.512%	$152.8236	$152.82	$152.80	$152.80
Purchase #4	$150.70	6.640%	$160.7065	$160.71	$160.70	$160.70
Purchase #5	$78.84	4.308%	$82.2364	$82.24	$82.25	$82.20
Purchase #6	$64.50	11.621%	$71.9955	$72.00	$72.00	$72.00
Purchase #7	$226.51	10.804%	$250.9821	$250.98	$251.00	$251.00
7 purchase totals =	$916.33		$987.8701	$987.88	$987.90	$987.80