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	$229.89	6.368%	$244.5294	$244.53	$244.55	$244.50
Purchase #2	$139.97	4.329%	$146.0293	$146.03	$146.05	$146.00
Purchase #3	$136.90	4.159%	$142.5937	$142.59	$142.60	$142.60
Purchase #4	$174.95	7.306%	$187.7318	$187.73	$187.75	$187.70
Purchase #5	$119.60	12.140%	$134.1194	$134.12	$134.10	$134.10
Purchase #6	$39.98	7.516%	$42.9849	$42.98	$43.00	$43.00
Purchase #7	$168.98	13.494%	$191.7822	$191.78	$191.80	$191.80
7 purchase totals =	$1,010.27		$1,089.7707	$1,089.76	$1,089.85	$1,089.70