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	$25.92	11.744%	$28.964	$28.96	$28.95	$29.00
Purchase #2	$209.64	4.478%	$219.0277	$219.03	$219.05	$219.00
Purchase #3	$100.63	11.196%	$111.8965	$111.90	$111.90	$111.90
Purchase #4	$103.98	5.497%	$109.6958	$109.70	$109.70	$109.70
Purchase #5	$239.39	10.673%	$264.9401	$264.94	$264.95	$264.90
Purchase #6	$53.49	5.655%	$56.5149	$56.51	$56.50	$56.50
Purchase #7	$109.92	12.793%	$123.9821	$123.98	$124.00	$124.00
7 purchase totals =	$842.97		$915.0211	$915.02	$915.05	$915.00