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	$161.34	4.673%	$168.8794	$168.88	$168.90	$168.90
Purchase #2	$28.92	12.530%	$32.5437	$32.54	$32.55	$32.50
Purchase #3	$81.41	9.726%	$89.3279	$89.33	$89.35	$89.30
Purchase #4	$24.79	8.685%	$26.943	$26.94	$26.95	$26.90
Purchase #5	$181.59	5.445%	$191.4776	$191.48	$191.50	$191.50
Purchase #6	$224.91	10.114%	$247.6574	$247.66	$247.65	$247.70
Purchase #7	$148.63	12.120%	$166.644	$166.64	$166.65	$166.60
7 purchase totals =	$851.59		$923.4730	$923.47	$923.55	$923.40