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	$85.38	3.773%	$88.6014	$88.60	$88.60	$88.60
Purchase #2	$156.37	6.750%	$166.925	$166.93	$166.95	$166.90
Purchase #3	$40.30	12.151%	$45.1969	$45.20	$45.20	$45.20
Purchase #4	$160.90	9.244%	$175.7736	$175.77	$175.75	$175.80
Purchase #5	$162.46	5.477%	$171.3579	$171.36	$171.35	$171.40
Purchase #6	$135.47	10.525%	$149.7282	$149.73	$149.75	$149.70
Purchase #7	$204.67	6.666%	$218.3133	$218.31	$218.30	$218.30
7 purchase totals =	$945.55		$1,015.8963	$1,015.90	$1,015.90	$1,015.90