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	$102.31	9.704%	$112.2382	$112.24	$112.25	$112.20
Purchase #2	$161.39	4.460%	$168.588	$168.59	$168.60	$168.60
Purchase #3	$170.25	11.609%	$190.0143	$190.01	$190.00	$190.00
Purchase #4	$62.34	13.143%	$70.5333	$70.53	$70.55	$70.50
Purchase #5	$222.53	12.573%	$250.5087	$250.51	$250.50	$250.50
Purchase #6	$17.83	6.210%	$18.9372	$18.94	$18.95	$18.90
Purchase #7	$102.58	9.818%	$112.6513	$112.65	$112.65	$112.70
7 purchase totals =	$839.23		$923.4710	$923.47	$923.50	$923.40