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	$133.70	8.118%	$144.5538	$144.55	$144.55	$144.60
Purchase #2	$210.98	5.615%	$222.8265	$222.83	$222.85	$222.80
Purchase #3	$222.53	13.120%	$251.7259	$251.73	$251.75	$251.70
Purchase #4	$132.86	7.248%	$142.4897	$142.49	$142.50	$142.50
Purchase #5	$245.34	12.452%	$275.8897	$275.89	$275.90	$275.90
Purchase #6	$30.97	6.592%	$33.0115	$33.01	$33.00	$33.00
Purchase #7	$109.83	5.450%	$115.8157	$115.82	$115.80	$115.80
7 purchase totals =	$1,086.21		$1,186.3128	$1,186.32	$1,186.35	$1,186.30