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	$33.76	10.179%	$37.1964	$37.20	$37.20	$37.20
Purchase #2	$56.66	4.636%	$59.2868	$59.29	$59.30	$59.30
Purchase #3	$64.29	12.819%	$72.5313	$72.53	$72.55	$72.50
Purchase #4	$117.40	6.289%	$124.7833	$124.78	$124.80	$124.80
Purchase #5	$112.78	3.769%	$117.0307	$117.03	$117.05	$117.00
Purchase #6	$141.28	5.218%	$148.652	$148.65	$148.65	$148.70
Purchase #7	$72.34	9.347%	$79.1016	$79.10	$79.10	$79.10
7 purchase totals =	$598.51		$638.5821	$638.58	$638.65	$638.60