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	$28.42	11.862%	$31.7912	$31.79	$31.80	$31.80
Purchase #2	$180.66	9.642%	$198.0792	$198.08	$198.10	$198.10
Purchase #3	$68.34	6.318%	$72.6577	$72.66	$72.65	$72.70
Purchase #4	$131.55	12.201%	$147.6004	$147.60	$147.60	$147.60
Purchase #5	$35.35	11.829%	$39.5316	$39.53	$39.55	$39.50
Purchase #6	$155.69	8.113%	$168.3211	$168.32	$168.30	$168.30
Purchase #7	$50.39	4.111%	$52.4615	$52.46	$52.45	$52.50
7 purchase totals =	$650.40		$710.4427	$710.44	$710.45	$710.50