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	$124.86	5.138%	$131.2753	$131.28	$131.30	$131.30
Purchase #2	$163.59	10.230%	$180.3253	$180.33	$180.35	$180.30
Purchase #3	$153.45	3.339%	$158.5737	$158.57	$158.55	$158.60
Purchase #4	$175.83	3.421%	$181.8451	$181.85	$181.85	$181.80
Purchase #5	$19.97	6.427%	$21.2535	$21.25	$21.25	$21.30
Purchase #6	$37.85	9.112%	$41.2989	$41.30	$41.30	$41.30
Purchase #7	$34.92	6.839%	$37.3082	$37.31	$37.30	$37.30
7 purchase totals =	$710.47		$751.8800	$751.89	$751.90	$751.90