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	$30.79	3.626%	$31.9064	$31.91	$31.90	$31.90
Purchase #2	$216.39	3.303%	$223.5374	$223.54	$223.55	$223.50
Purchase #3	$215.45	3.713%	$223.4497	$223.45	$223.45	$223.40
Purchase #4	$224.90	7.260%	$241.2277	$241.23	$241.25	$241.20
Purchase #5	$221.61	7.750%	$238.7848	$238.78	$238.80	$238.80
Purchase #6	$137.94	4.550%	$144.2163	$144.22	$144.20	$144.20
Purchase #7	$94.51	5.726%	$99.9216	$99.92	$99.90	$99.90
7 purchase totals =	$1,141.59		$1,203.0439	$1,203.05	$1,203.05	$1,202.90