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	$45.61	11.218%	$50.7265	$50.73	$50.75	$50.70
Purchase #2	$190.95	9.541%	$209.1685	$209.17	$209.15	$209.20
Purchase #3	$222.27	13.135%	$251.4652	$251.47	$251.45	$251.50
Purchase #4	$75.66	10.488%	$83.5952	$83.60	$83.60	$83.60
Purchase #5	$164.88	6.854%	$176.1809	$176.18	$176.20	$176.20
Purchase #6	$61.37	5.259%	$64.5974	$64.60	$64.60	$64.60
Purchase #7	$162.82	3.784%	$168.9811	$168.98	$169.00	$169.00
7 purchase totals =	$923.56		$1,004.7148	$1,004.73	$1,004.75	$1,004.80