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	$218.49	8.275%	$236.57	$236.57	$236.55	$236.60
Purchase #2	$123.69	13.815%	$140.7778	$140.78	$140.80	$140.80
Purchase #3	$78.48	5.636%	$82.9031	$82.90	$82.90	$82.90
Purchase #4	$139.78	9.772%	$153.4393	$153.44	$153.45	$153.40
Purchase #5	$93.31	10.620%	$103.2195	$103.22	$103.20	$103.20
Purchase #6	$196.94	7.789%	$212.2797	$212.28	$212.30	$212.30
Purchase #7	$85.77	6.603%	$91.4334	$91.43	$91.45	$91.40
7 purchase totals =	$936.46		$1,020.6228	$1,020.62	$1,020.65	$1,020.60