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	$64.73	10.784%	$71.7105	$71.71	$71.70	$71.70
Purchase #2	$78.96	7.850%	$85.1584	$85.16	$85.15	$85.20
Purchase #3	$250.50	3.318%	$258.8116	$258.81	$258.80	$258.80
Purchase #4	$27.27	8.507%	$29.5899	$29.59	$29.60	$29.60
Purchase #5	$162.55	11.123%	$180.6304	$180.63	$180.65	$180.60
Purchase #6	$162.34	4.530%	$169.694	$169.69	$169.70	$169.70
Purchase #7	$180.27	4.473%	$188.3335	$188.33	$188.35	$188.30
7 purchase totals =	$926.62		$983.9283	$983.92	$983.95	$983.90