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	$82.35	10.220%	$90.7662	$90.77	$90.75	$90.80
Purchase #2	$147.48	13.694%	$167.6759	$167.68	$167.70	$167.70
Purchase #3	$161.85	6.846%	$172.9303	$172.93	$172.95	$172.90
Purchase #4	$230.97	7.810%	$249.0088	$249.01	$249.00	$249.00
Purchase #5	$70.47	13.191%	$79.7657	$79.77	$79.75	$79.80
Purchase #6	$242.59	10.782%	$268.7461	$268.75	$268.75	$268.70
Purchase #7	$81.74	4.690%	$85.5736	$85.57	$85.55	$85.60
7 purchase totals =	$1,017.45		$1,114.4666	$1,114.48	$1,114.45	$1,114.50