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	$47.53	8.846%	$51.7345	$51.73	$51.75	$51.70
Purchase #2	$110.69	6.476%	$117.8583	$117.86	$117.85	$117.90
Purchase #3	$37.52	7.795%	$40.4447	$40.44	$40.45	$40.40
Purchase #4	$89.28	3.229%	$92.1629	$92.16	$92.15	$92.20
Purchase #5	$168.53	7.441%	$181.0703	$181.07	$181.05	$181.10
Purchase #6	$39.46	4.305%	$41.1588	$41.16	$41.15	$41.20
Purchase #7	$167.52	9.141%	$182.833	$182.83	$182.85	$182.80
7 purchase totals =	$660.53		$707.2625	$707.25	$707.25	$707.30