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	$128.44	3.818%	$133.3438	$133.34	$133.35	$133.30
Purchase #2	$210.45	4.126%	$219.1332	$219.13	$219.15	$219.10
Purchase #3	$99.55	6.382%	$105.9033	$105.90	$105.90	$105.90
Purchase #4	$31.53	9.173%	$34.4222	$34.42	$34.40	$34.40
Purchase #5	$145.59	12.550%	$163.8615	$163.86	$163.85	$163.90
Purchase #6	$125.43	5.166%	$131.9097	$131.91	$131.90	$131.90
Purchase #7	$80.48	11.507%	$89.7408	$89.74	$89.75	$89.70
7 purchase totals =	$821.47		$878.3145	$878.30	$878.30	$878.20