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	$134.35	11.469%	$149.7586	$149.76	$149.75	$149.80
Purchase #2	$137.61	9.592%	$150.8096	$150.81	$150.80	$150.80
Purchase #3	$151.72	10.523%	$167.6855	$167.69	$167.70	$167.70
Purchase #4	$40.73	4.303%	$42.4826	$42.48	$42.50	$42.50
Purchase #5	$194.40	12.334%	$218.3773	$218.38	$218.40	$218.40
Purchase #6	$83.40	8.303%	$90.3247	$90.32	$90.30	$90.30
Purchase #7	$55.90	4.266%	$58.2847	$58.28	$58.30	$58.30
7 purchase totals =	$798.11		$877.7230	$877.72	$877.75	$877.80