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	$31.58	5.640%	$33.3611	$33.36	$33.35	$33.40
Purchase #2	$141.63	10.366%	$156.3114	$156.31	$156.30	$156.30
Purchase #3	$64.86	9.540%	$71.0476	$71.05	$71.05	$71.00
Purchase #4	$91.83	7.550%	$98.7632	$98.76	$98.75	$98.80
Purchase #5	$207.67	12.301%	$233.2155	$233.22	$233.20	$233.20
Purchase #6	$180.69	6.611%	$192.6354	$192.64	$192.65	$192.60
Purchase #7	$84.73	6.799%	$90.4908	$90.49	$90.50	$90.50
7 purchase totals =	$802.99		$875.8250	$875.83	$875.80	$875.80