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	$142.98	11.276%	$159.1024	$159.10	$159.10	$159.10
Purchase #2	$146.43	10.778%	$162.2122	$162.21	$162.20	$162.20
Purchase #3	$129.76	12.376%	$145.8191	$145.82	$145.80	$145.80
Purchase #4	$196.26	10.121%	$216.1235	$216.12	$216.10	$216.10
Purchase #5	$97.37	12.743%	$109.7779	$109.78	$109.80	$109.80
Purchase #6	$77.42	4.392%	$80.8203	$80.82	$80.80	$80.80
Purchase #7	$39.57	4.472%	$41.3396	$41.34	$41.35	$41.30
7 purchase totals =	$829.79		$915.1950	$915.19	$915.15	$915.10