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	$40.40	6.106%	$42.8668	$42.87	$42.85	$42.90
Purchase #2	$110.31	9.512%	$120.8027	$120.80	$120.80	$120.80
Purchase #3	$157.29	7.671%	$169.3557	$169.36	$169.35	$169.40
Purchase #4	$144.61	13.829%	$164.6081	$164.61	$164.60	$164.60
Purchase #5	$220.43	9.516%	$241.4061	$241.41	$241.40	$241.40
Purchase #6	$133.37	6.688%	$142.2898	$142.29	$142.30	$142.30
Purchase #7	$209.41	4.447%	$218.7225	$218.72	$218.70	$218.70
7 purchase totals =	$1,015.82		$1,100.0517	$1,100.06	$1,100.00	$1,100.10