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	$238.27	3.790%	$247.3004	$247.30	$247.30	$247.30
Purchase #2	$189.90	12.320%	$213.2957	$213.30	$213.30	$213.30
Purchase #3	$177.59	13.120%	$200.8898	$200.89	$200.90	$200.90
Purchase #4	$248.81	8.280%	$269.4115	$269.41	$269.40	$269.40
Purchase #5	$48.78	3.530%	$50.5019	$50.50	$50.50	$50.50
Purchase #6	$190.60	11.245%	$212.033	$212.03	$212.05	$212.00
Purchase #7	$167.48	7.200%	$179.5386	$179.54	$179.55	$179.50
7 purchase totals =	$1,261.43		$1,372.9709	$1,372.97	$1,373.00	$1,372.90