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	$66.63	3.337%	$68.8534	$68.85	$68.85	$68.90
Purchase #2	$52.65	9.779%	$57.7986	$57.80	$57.80	$57.80
Purchase #3	$159.27	7.732%	$171.5848	$171.58	$171.60	$171.60
Purchase #4	$14.25	5.312%	$15.007	$15.01	$15.00	$15.00
Purchase #5	$181.89	5.428%	$191.763	$191.76	$191.75	$191.80
Purchase #6	$169.33	3.245%	$174.8248	$174.82	$174.80	$174.80
Purchase #7	$99.90	9.413%	$109.3036	$109.30	$109.30	$109.30
7 purchase totals =	$743.92		$789.1352	$789.12	$789.10	$789.20