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	$120.86	9.710%	$132.5955	$132.60	$132.60	$132.60
Purchase #2	$238.98	4.857%	$250.5873	$250.59	$250.60	$250.60
Purchase #3	$91.86	3.121%	$94.727	$94.73	$94.75	$94.70
Purchase #4	$224.72	11.296%	$250.1044	$250.10	$250.10	$250.10
Purchase #5	$250.78	12.265%	$281.5382	$281.54	$281.55	$281.50
Purchase #6	$175.35	5.629%	$185.2205	$185.22	$185.20	$185.20
Purchase #7	$6.45	10.331%	$7.1163	$7.12	$7.10	$7.10
7 purchase totals =	$1,109.00		$1,201.8892	$1,201.90	$1,201.90	$1,201.80