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	$171.42	12.167%	$192.2767	$192.28	$192.30	$192.30
Purchase #2	$147.52	11.279%	$164.1588	$164.16	$164.15	$164.20
Purchase #3	$96.46	3.620%	$99.9519	$99.95	$99.95	$100.00
Purchase #4	$5.78	8.874%	$6.2929	$6.29	$6.30	$6.30
Purchase #5	$35.26	11.755%	$39.4048	$39.40	$39.40	$39.40
Purchase #6	$250.69	12.799%	$282.7758	$282.78	$282.80	$282.80
Purchase #7	$100.87	11.618%	$112.5891	$112.59	$112.60	$112.60
7 purchase totals =	$808.00		$897.4500	$897.45	$897.50	$897.60