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	$54.37	6.719%	$58.0231	$58.02	$58.00	$58.00
Purchase #2	$132.32	11.404%	$147.4098	$147.41	$147.40	$147.40
Purchase #3	$175.69	5.781%	$185.8466	$185.85	$185.85	$185.80
Purchase #4	$37.51	7.547%	$40.3409	$40.34	$40.35	$40.30
Purchase #5	$5.84	9.156%	$6.3747	$6.37	$6.35	$6.40
Purchase #6	$28.82	9.111%	$31.4458	$31.45	$31.45	$31.40
Purchase #7	$47.86	7.283%	$51.3456	$51.35	$51.35	$51.30
7 purchase totals =	$482.41		$520.7865	$520.79	$520.75	$520.60