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	$248.39	10.148%	$273.5966	$273.60	$273.60	$273.60
Purchase #2	$24.96	6.370%	$26.55	$26.55	$26.55	$26.60
Purchase #3	$142.88	6.661%	$152.3972	$152.40	$152.40	$152.40
Purchase #4	$75.25	9.856%	$82.6666	$82.67	$82.65	$82.70
Purchase #5	$238.47	5.544%	$251.6908	$251.69	$251.70	$251.70
Purchase #6	$31.48	7.560%	$33.8599	$33.86	$33.85	$33.90
Purchase #7	$249.78	7.543%	$268.6209	$268.62	$268.60	$268.60
7 purchase totals =	$1,011.21		$1,089.3820	$1,089.39	$1,089.35	$1,089.50