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	$240.78	11.274%	$267.9255	$267.93	$267.95	$267.90
Purchase #2	$191.86	4.521%	$200.534	$200.53	$200.55	$200.50
Purchase #3	$54.39	9.338%	$59.4689	$59.47	$59.45	$59.50
Purchase #4	$162.63	6.430%	$173.0871	$173.09	$173.10	$173.10
Purchase #5	$61.89	11.344%	$68.9108	$68.91	$68.90	$68.90
Purchase #6	$90.62	7.645%	$97.5479	$97.55	$97.55	$97.50
Purchase #7	$70.47	11.764%	$78.7601	$78.76	$78.75	$78.80
7 purchase totals =	$872.64		$946.2343	$946.24	$946.25	$946.20