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	$247.58	13.550%	$281.1271	$281.13	$281.15	$281.10
Purchase #2	$39.49	9.581%	$43.2735	$43.27	$43.25	$43.30
Purchase #3	$193.46	3.814%	$200.8386	$200.84	$200.85	$200.80
Purchase #4	$218.39	11.329%	$243.1314	$243.13	$243.15	$243.10
Purchase #5	$52.32	5.588%	$55.2436	$55.24	$55.25	$55.20
Purchase #6	$74.87	4.678%	$78.3724	$78.37	$78.35	$78.40
Purchase #7	$82.70	4.595%	$86.5001	$86.50	$86.50	$86.50
7 purchase totals =	$908.81		$988.4867	$988.48	$988.50	$988.40