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	$87.93	13.816%	$100.0784	$100.08	$100.10	$100.10
Purchase #2	$36.38	10.482%	$40.1934	$40.19	$40.20	$40.20
Purchase #3	$127.90	7.243%	$137.1638	$137.16	$137.15	$137.20
Purchase #4	$97.76	4.214%	$101.8796	$101.88	$101.90	$101.90
Purchase #5	$58.26	10.689%	$64.4874	$64.49	$64.50	$64.50
Purchase #6	$172.51	9.873%	$189.5419	$189.54	$189.55	$189.50
Purchase #7	$160.55	13.671%	$182.4988	$182.50	$182.50	$182.50
7 purchase totals =	$741.29		$815.8433	$815.84	$815.90	$815.90