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	$139.46	6.127%	$148.0047	$148.00	$148.00	$148.00
Purchase #2	$195.37	6.784%	$208.6239	$208.62	$208.60	$208.60
Purchase #3	$90.77	11.157%	$100.8972	$100.90	$100.90	$100.90
Purchase #4	$39.76	4.360%	$41.4935	$41.49	$41.50	$41.50
Purchase #5	$188.73	8.405%	$204.5928	$204.59	$204.60	$204.60
Purchase #6	$93.93	13.147%	$106.279	$106.28	$106.30	$106.30
Purchase #7	$123.31	3.731%	$127.9107	$127.91	$127.90	$127.90
7 purchase totals =	$871.33		$937.8018	$937.79	$937.80	$937.80