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	$53.85	3.534%	$55.7531	$55.75	$55.75	$55.80
Purchase #2	$177.37	5.364%	$186.8841	$186.88	$186.90	$186.90
Purchase #3	$129.27	8.407%	$140.1377	$140.14	$140.15	$140.10
Purchase #4	$19.71	11.693%	$22.0147	$22.01	$22.00	$22.00
Purchase #5	$86.28	3.642%	$89.4223	$89.42	$89.40	$89.40
Purchase #6	$87.70	12.754%	$98.8853	$98.89	$98.90	$98.90
Purchase #7	$32.87	13.723%	$37.3808	$37.38	$37.40	$37.40
7 purchase totals =	$587.05		$630.4780	$630.47	$630.50	$630.50