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	$136.56	6.751%	$145.7792	$145.78	$145.80	$145.80
Purchase #2	$104.38	7.865%	$112.5895	$112.59	$112.60	$112.60
Purchase #3	$149.41	12.658%	$168.3223	$168.32	$168.30	$168.30
Purchase #4	$196.43	13.767%	$223.4725	$223.47	$223.45	$223.50
Purchase #5	$225.92	11.452%	$251.7924	$251.79	$251.80	$251.80
Purchase #6	$138.79	12.241%	$155.7793	$155.78	$155.80	$155.80
Purchase #7	$108.37	8.486%	$117.5663	$117.57	$117.55	$117.60
7 purchase totals =	$1,059.86		$1,175.3015	$1,175.30	$1,175.30	$1,175.40