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	$107.26	4.819%	$112.4289	$112.43	$112.45	$112.40
Purchase #2	$178.56	6.183%	$189.6004	$189.60	$189.60	$189.60
Purchase #3	$174.74	13.494%	$198.3194	$198.32	$198.30	$198.30
Purchase #4	$229.95	4.603%	$240.5346	$240.53	$240.55	$240.50
Purchase #5	$54.40	9.595%	$59.6197	$59.62	$59.60	$59.60
Purchase #6	$82.31	11.642%	$91.8925	$91.89	$91.90	$91.90
Purchase #7	$81.37	10.718%	$90.0912	$90.09	$90.10	$90.10
7 purchase totals =	$908.59		$982.4867	$982.48	$982.50	$982.40