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	$42.69	5.660%	$45.1063	$45.11	$45.10	$45.10
Purchase #2	$240.93	4.521%	$251.8224	$251.82	$251.80	$251.80
Purchase #3	$23.46	3.654%	$24.3172	$24.32	$24.30	$24.30
Purchase #4	$131.43	8.442%	$142.5253	$142.53	$142.55	$142.50
Purchase #5	$210.99	5.138%	$221.8307	$221.83	$221.85	$221.80
Purchase #6	$153.86	9.423%	$168.3582	$168.36	$168.35	$168.40
Purchase #7	$194.86	8.476%	$211.3763	$211.38	$211.40	$211.40
7 purchase totals =	$998.22		$1,065.3364	$1,065.35	$1,065.35	$1,065.30