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	$227.75	5.618%	$240.545	$240.55	$240.55	$240.50
Purchase #2	$55.39	7.199%	$59.3775	$59.38	$59.40	$59.40
Purchase #3	$143.96	4.825%	$150.9061	$150.91	$150.90	$150.90
Purchase #4	$109.85	9.709%	$120.5153	$120.52	$120.50	$120.50
Purchase #5	$53.30	13.476%	$60.4827	$60.48	$60.50	$60.50
Purchase #6	$205.96	9.607%	$225.7466	$225.75	$225.75	$225.70
Purchase #7	$111.44	12.499%	$125.3689	$125.37	$125.35	$125.40
7 purchase totals =	$907.65		$982.9421	$982.96	$982.95	$982.90