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	$72.36	9.720%	$79.3934	$79.39	$79.40	$79.40
Purchase #2	$152.76	11.236%	$169.9241	$169.92	$169.90	$169.90
Purchase #3	$39.94	6.506%	$42.5385	$42.54	$42.55	$42.50
Purchase #4	$62.85	6.860%	$67.1615	$67.16	$67.15	$67.20
Purchase #5	$242.91	10.433%	$268.2528	$268.25	$268.25	$268.30
Purchase #6	$38.39	10.805%	$42.538	$42.54	$42.55	$42.50
Purchase #7	$150.54	6.196%	$159.8675	$159.87	$159.85	$159.90
7 purchase totals =	$759.75		$829.6758	$829.67	$829.65	$829.70