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	$109.56	13.157%	$123.9748	$123.97	$123.95	$124.00
Purchase #2	$95.69	4.535%	$100.0295	$100.03	$100.05	$100.00
Purchase #3	$165.83	9.177%	$181.0482	$181.05	$181.05	$181.00
Purchase #4	$243.59	10.410%	$268.9477	$268.95	$268.95	$268.90
Purchase #5	$169.83	7.818%	$183.1073	$183.11	$183.10	$183.10
Purchase #6	$29.44	11.380%	$32.7903	$32.79	$32.80	$32.80
Purchase #7	$141.39	4.857%	$148.2573	$148.26	$148.25	$148.30
7 purchase totals =	$955.33		$1,038.1551	$1,038.16	$1,038.15	$1,038.10