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	$54.81	7.604%	$58.9778	$58.98	$59.00	$59.00
Purchase #2	$119.60	9.867%	$131.4009	$131.40	$131.40	$131.40
Purchase #3	$121.48	7.487%	$130.5752	$130.58	$130.60	$130.60
Purchase #4	$84.47	8.748%	$91.8594	$91.86	$91.85	$91.90
Purchase #5	$69.56	13.144%	$78.703	$78.70	$78.70	$78.70
Purchase #6	$64.36	12.425%	$72.3567	$72.36	$72.35	$72.40
Purchase #7	$250.44	9.196%	$273.4705	$273.47	$273.45	$273.50
7 purchase totals =	$764.72		$837.3435	$837.35	$837.35	$837.50