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	$242.82	3.311%	$250.8598	$250.86	$250.85	$250.90
Purchase #2	$160.25	4.830%	$167.9901	$167.99	$168.00	$168.00
Purchase #3	$72.91	10.464%	$80.5393	$80.54	$80.55	$80.50
Purchase #4	$158.82	4.722%	$166.3195	$166.32	$166.30	$166.30
Purchase #5	$97.42	6.656%	$103.9043	$103.90	$103.90	$103.90
Purchase #6	$135.57	11.603%	$151.3002	$151.30	$151.30	$151.30
Purchase #7	$71.97	11.532%	$80.2696	$80.27	$80.25	$80.30
7 purchase totals =	$939.76		$1,001.1828	$1,001.18	$1,001.15	$1,001.20