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	$129.34	7.408%	$138.9215	$138.92	$138.90	$138.90
Purchase #2	$6.88	6.815%	$7.3489	$7.35	$7.35	$7.30
Purchase #3	$135.91	6.229%	$144.3758	$144.38	$144.40	$144.40
Purchase #4	$229.83	11.778%	$256.8994	$256.90	$256.90	$256.90
Purchase #5	$118.75	10.510%	$131.2306	$131.23	$131.25	$131.20
Purchase #6	$58.86	11.503%	$65.6307	$65.63	$65.65	$65.60
Purchase #7	$198.30	10.671%	$219.4606	$219.46	$219.45	$219.50
7 purchase totals =	$877.87		$963.8675	$963.87	$963.90	$963.80