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	$145.53	7.196%	$156.0023	$156.00	$156.00	$156.00
Purchase #2	$64.34	11.735%	$71.8903	$71.89	$71.90	$71.90
Purchase #3	$53.67	3.177%	$55.3751	$55.38	$55.40	$55.40
Purchase #4	$67.65	11.721%	$75.5793	$75.58	$75.60	$75.60
Purchase #5	$198.50	7.765%	$213.9135	$213.91	$213.90	$213.90
Purchase #6	$166.58	11.177%	$185.1986	$185.20	$185.20	$185.20
Purchase #7	$136.39	3.613%	$141.3178	$141.32	$141.30	$141.30
7 purchase totals =	$832.66		$899.2769	$899.28	$899.30	$899.30