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	$219.36	12.108%	$245.9201	$245.92	$245.90	$245.90
Purchase #2	$91.59	12.718%	$103.2384	$103.24	$103.25	$103.20
Purchase #3	$93.49	3.262%	$96.5396	$96.54	$96.55	$96.50
Purchase #4	$145.83	13.822%	$165.9866	$165.99	$166.00	$166.00
Purchase #5	$95.87	12.804%	$108.1452	$108.15	$108.15	$108.10
Purchase #6	$72.96	7.737%	$78.6049	$78.60	$78.60	$78.60
Purchase #7	$230.34	9.331%	$251.833	$251.83	$251.85	$251.80
7 purchase totals =	$949.44		$1,050.2678	$1,050.27	$1,050.30	$1,050.10