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	$137.65	3.629%	$142.6453	$142.65	$142.65	$142.60
Purchase #2	$77.98	4.397%	$81.4088	$81.41	$81.40	$81.40
Purchase #3	$142.38	6.586%	$151.7571	$151.76	$151.75	$151.80
Purchase #4	$181.58	7.455%	$195.1168	$195.12	$195.10	$195.10
Purchase #5	$166.61	3.148%	$171.8549	$171.85	$171.85	$171.90
Purchase #6	$208.89	7.847%	$225.2816	$225.28	$225.30	$225.30
Purchase #7	$123.97	6.308%	$131.79	$131.79	$131.80	$131.80
7 purchase totals =	$1,039.06		$1,099.8545	$1,099.86	$1,099.85	$1,099.90