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	$93.86	12.179%	$105.2912	$105.29	$105.30	$105.30
Purchase #2	$118.43	8.153%	$128.0856	$128.09	$128.10	$128.10
Purchase #3	$246.33	6.343%	$261.9547	$261.95	$261.95	$262.00
Purchase #4	$26.88	7.659%	$28.9387	$28.94	$28.95	$28.90
Purchase #5	$82.30	10.522%	$90.9596	$90.96	$90.95	$91.00
Purchase #6	$240.34	4.200%	$250.4343	$250.43	$250.45	$250.40
Purchase #7	$103.96	13.586%	$118.084	$118.08	$118.10	$118.10
7 purchase totals =	$912.10		$983.7481	$983.74	$983.80	$983.80