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	$78.83	4.860%	$82.6611	$82.66	$82.65	$82.70
Purchase #2	$91.77	11.755%	$102.5576	$102.56	$102.55	$102.60
Purchase #3	$75.39	11.260%	$83.8789	$83.88	$83.90	$83.90
Purchase #4	$83.37	8.436%	$90.4031	$90.40	$90.40	$90.40
Purchase #5	$168.54	5.540%	$177.8771	$177.88	$177.90	$177.90
Purchase #6	$250.35	7.446%	$268.9911	$268.99	$269.00	$269.00
Purchase #7	$100.34	8.467%	$108.8358	$108.84	$108.85	$108.80
7 purchase totals =	$848.59		$915.2047	$915.21	$915.25	$915.30