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	$223.88	4.160%	$233.1934	$233.19	$233.20	$233.20
Purchase #2	$49.58	7.589%	$53.3426	$53.34	$53.35	$53.30
Purchase #3	$127.79	7.750%	$137.6937	$137.69	$137.70	$137.70
Purchase #4	$33.84	13.346%	$38.3563	$38.36	$38.35	$38.40
Purchase #5	$240.89	9.372%	$263.4662	$263.47	$263.45	$263.50
Purchase #6	$31.87	4.753%	$33.3848	$33.38	$33.40	$33.40
Purchase #7	$209.61	4.636%	$219.3275	$219.33	$219.35	$219.30
7 purchase totals =	$917.46		$978.7645	$978.76	$978.80	$978.80